Session: 50-State Update of the USGS National Seismic Hazard Models

Type: Oral

Room: Grand E-K

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Mark D. Petersen

Description

We are developing the 2023 U.S. National Seismic Hazard Model for all 50 states by applying new seismicity, fault rupture models and ground motion assessments. We consider two types of models: (1) a public model that guides hazard assessments intended for building code provisions and policy applications and (2) a research model geared towards less formal applications that may be included in future public models. New data and methods will be introduced in the 2023 earthquake source components: earthquake catalogs - excluding induced earthquakes, alternative declustering methods, spatially smoothed seismicity, scaled rates to account for aftershocks, new geodetic and geologic data and fault rupture models accounting for a more complete representation of potential earthquakes in Alaska, Hawaii and the conterminous U.S. Improved ground motion models (GMMs) consider new NGA-Subduction, modified NGA-East and NGA-West2, as well as other published models. Some NGA-subduction and earthquake source models contain changes in median and aleatory variability that need to be evaluated and weighted. Basin amplification models will also consider 3D simulations with potential modifications at basin edges. Preliminary assessments indicate several relatively shallow Intermountain-West basins exhibit greater long-period amplifications than estimated by NGA-West2, potentially warranting additional basin-specific observations and simulations. New stress drop, tomographic and other geophysical models help refine the complex boundary between the tectonically stable and active regions used in assigning GMMs. The research model may incorporate more geological information on timing of past earthquakes for a time-dependent assessment and regional variations in earthquake shaking accounting for a partially non-ergodic ground motion representation. Scenarios and population exposure assessments of these models will help users assess impacts of the earthquakes.

Additional Authors

Session: Frontiers in Earthquake and Tsunami Science - Model Integration, Recent Advances, Ongoing Questions

Type: Oral

Room: Grand C

Date: 4/22/2022

Presentation Time: 09:00 AM Pacific

Presenting Author: Alice-Agnes Gabriel

Description

While tsunamis occur due to abrupt vertical perturbations to the water column, a devastating tsunami was caused by the strike-slip, supershear 2018, Palu, Sulawesi earthquake. Studying such surprising earthquake-tsunami behavior has been hampered by the necessity of making approximations in the fluid-solid coupling. Recent simulations (Ulrich et al., 2019) suggest that the Palu tsunami can be primarily understood from the complex interaction of transtensional earthquake rupture dynamics across a geometrically complex strike-slip fault system and the 3D bay bathymetry. However, the standard practice of linking a 3D earthquake simulation, conducted without a water layer, to a 2D tsunami shallow water model simplifies the interaction between the ocean floor and water column.

We develop a highly scalable 3D fully-coupled Earth and ocean model of earthquake rupture and tsunami generation implemented in SeisSol (Krenz et al., 2021). We model seismic, acoustic and surface gravity wave propagation sourced by physics-based non-linear earthquake dynamic rupture, naturally capturing tsunami dispersion and related nonhydrostatic effects during both tsunami generation and propagation. Multi-petascale simulations, with excellent performance on three different supercomputers, allow to include complicated geometries, such as high-resolution bathymetry, coastlines and segmented earthquake faults. We present the first fully coupled simulation of an actual earthquake-tsunami event and a 3D benchmark problem of tsunami generation by a megathrust dynamic earthquake rupture. There are notable differences in the fully coupled and 3D-2D linked models for the Palu event, potentially due to the non-hydrostatic ocean response and the complex, high-frequency source. Our work enables us to capture the entire dynamics of this process in an efficient, unified 3D model and our predictions of pressure changes in the water column, including at the seafloor, may help to interpret ocean bottom pressure sensor data containing more than just tsunami waves.

Additional Authors

Session: Advances in Seismoacoustic Methods for Explosion Monitoring I

Type: Oral

Room: Cedar

Date: 4/22/2022

Presentation Time: 08:45 AM Pacific

Presenting Author: Jeffry Stevens

Description

Understanding of the explosion source is fundamental to nuclear monitoring. In spite of decades of research on this subject, there are still many unknowns, particularly when there is strong topography, tectonic stresses or multiple simultaneous explosions. We have developed a 3D Lagrangian Finite Element Code, CRAM3D, that allows calculations of complex explosion emplacement conditions and can directly address these problems. CRAM3D has been developed over more than a decade, but the history of the code is actually much longer, as it was derived from an earlier axisymmetric code CRAM developed during the nuclear containment program. Although the structure of CRAM3D is more modern and quite different, CRAM3D includes material models from CRAM that were developed over many years based on nuclear explosion data. The output of CRAM3D interfaces with code that uses the representation theorem to propagate the near-source motion to regional and teleseismic distances.

CRAM3D uses MPI to split a calculation over multiple processors and so has the capability to address very large problems. It has been used recently to model explosions at the North Korean Test Site, where topography strongly affects seismic waves; to model 13 explosions at the Degelen Mountain test site, where topography and tectonic stresses are important; and to model explosions at the Novaya Zemlya test site, which has both strong topography and multiple simultaneous explosions.

Additional Authors

Session: Development, Enhancement and Validation of Seismic Velocity Models [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Jennifer L. Harding

Description

The Rock Valley Fault Zone (RVFZ) is a ~4 km-wide group of active, left-lateral strike slip faults that trend northeast within Rock Valley (RV), in the southern Nevada National Security Site. The RVFZ has hosted a number of magnitude > 3 events, and in May 1993, a shallow (< 3 km) magnitude 3.7 event occurred at the RVFZ and triggered over 600 aftershocks in the five months following. Precise hypocentral locations require a local seismic study in order to refine seismic velocities and constrain the faults at depth. We conducted an active-source accelerated weight drop (AWD) experiment over the central RVFZ area in April and May of 2021. We deployed 188 3-component seismometers along several intersecting transects at ~100 m spacing and recorded 553 AWD vertical and side hits. The waveform data were processed into shot gathers from which we picked P- and S-wave travel-times. We then inverted these picked travel-times for 3D P-wave velocity (Vp) and S-wave velocity (Vs) structure using a linearized, iterative, least squares inversion scheme. We resolved velocities as deep as 600 m, with Vp and Vs structure consistent with the local geology of the RVFZ. We imaged lower velocities at depth to the northwest in a volcanic domain and higher velocities to the southeast in a carbonate domain, with Vp reaching 3 km/s at ~200 m below the surface to the northwest and ~150 m below the surface to the southeast. Just to the north of, and bounded by, the central fault strands is a lower velocity region that is ~ 1 km wide and persists to the deepest part of the velocity model. Vp in this region reaches 3 km/s at ~300 m below the surface. The lower velocity region could be caused by enhanced faulting and fracturing. These local 3D Vp and Vs models will be incorporated into regional models to be used for more precise earthquake hypocentral locations.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525

Additional Authors

Session: Advances in Seismoacoustic Methods for Explosion Monitoring II

Type: Oral

Room: Cedar

Date: 4/22/2022

Presentation Time: 10:15 AM Pacific

Presenting Author: Carene Larmat

Description

Shear wave energy has been observed for most underground explosions which are classically modeled as isotropic sources. Shear waves are likely to be produced by any deviation of the actual source from an ideal isotropic source and by wave propagation in a complex subsurface where reflections and refraction will transfer seismic energy from P to S-wave. In this study, we use 3D full waveform modeling enabled by the code SPECFEM3D (Komatitsch & Tromp, 1999) to quantify the effect of different subsurface features on P/S ratio. Our goal is to explain some of the scatter observed for P/S ratio for small events and at short event-to-station distances that challenges discrimination methods (Pyle & Walter, 2019). SPECFEM3D is based on the Spectral Element Method (SEM) which is a direct numerical method that has benefited from advances in numerical methods and (super)computers over the last two decades.

Our modeling is compared to data recorded by a dense Large-N array of a series of well-instrumented chemical explosions in the Yucca Flat basin (Nevada), Phase II of the Source Physics Experiment (SPE). The four explosions of the series were carried-out in quaternary alluvium overlying tertiary tuff and Paleozoic basement rocks. A subsurface model was built using a local geological framework model and different models of seismic velocities were tested, some coming from seismic analyses, some from tomographic studies. We further varied the velocity of each geological unit in the model using Gaussian and Von Karman distributions to account for random heterogeneities. The accuracy of our modeling is assessed with different convergence tests. We compare modeled P/S ratios and peak velocities of the transverse component to the data to constraint our modeling. We found that the contrast between the tuff and the sedimentary layer is key in matching the peak velocity of the transverse component observed in the data with synthetics.

Additional Authors

Session: Numerical Modeling in Seismology: Developments and Applications I

Type: Oral

Room: Regency A-C

Date: 4/20/2022

Presentation Time: 08:30 AM Pacific

Presenting Author: Te-Yang Yeh

Description

Assessment of seismic hazard for embankment dams is crucial since they are typically built from compacted soils and rocks, which make them more prone to failure than concrete dams during strong ground shaking. As a case study, we conducted 3D 0-7.5 Hz deterministic wave propagation simulations to model realistic seismic response of the Long Valley Dam (LVD) in Central California using the discontinuous-mesh, fourth order accurate finite difference code AWP-ODC. Our goal is to account for the nonlinear effects in the time domain in order to adequately describe the complete seismic response of the dam during the extended duration of ground motions generated by large earthquakes. As the first step, we calibrated the velocity structure, anelastic attenuation model and the overall properties of the dam by performing linear simulations of an Mw 3.7 event using a point source. In our validation work we showed that accurate near-surface geotechnical layers are crucial to match observed ground motions at high frequencies (above 1Hz). A homogeneous model of the compacted dam core is sufficient for reproducing seismic waveforms observed right on the dam structure. A velocity-dependent attenuation model of Qs=0.075Vs, Qp=2Qs with a power law exponent of 0.2 for the frequency dependence best describes the observed spectral characteristics and coda wave amplitudes. With the calibrated model, we simulated the 1986 Mw6.3 Chalfant Valley earthquake, located 30 km from the LVD, using a finite-fault source description. Our simulations produced waveforms similar to the observations, with minimal nonlinearity needed around the LVD. Finally, we will present results of nonlinear simulations of Mw6.6 Maximum Credible Earthquake scenarios on the Hilton Creek fault, located within 10 km of the LVD.

Additional Authors

Session: Development, Enhancement and Validation of Seismic Velocity Models [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Ian Stone

Description

The U.S. Geological Survey's 3-D Cascadia Seismic Velocity Model (CVM) is commonly used to describe Earth structure when simulating earthquakes in western Washington, Oregon and Northern California. By considering results from seismic tomography surveys and regional geologic mapping, the CVM reasonably constrains seismic velocity throughout the region. However, the model does not include a geotechnical layer and has only rudimentary shallow (<100 m depth) velocity information. In preparation for high frequency (>1 Hz), direct earthquake simulations, we make targeted updates to the CVM to account for greater near-surface and near-fault complexity. These updates include adding surface topography, a shallow, low-velocity (~100 m/s) geotechnical layer, and near-fault damage zones. The updates are made in addition to imposing a frequency-independent attenuation model and small-scale, S-wave velocity heterogeneity throughout the shallow crust. We investigate the impact of these changes by simulating a suite of M6.5+, kinematic rupture scenarios on the Tacoma Fault, a crustal reverse fault in Washington State’s Puget Sound region. Simulations are run in 3-D using a spectral element method code (SPECFEM3D) on a mesh with a finely sampled topographic surface. The resulting ground motions can be resolved up to 3 Hz. We compare simulated ground motions between the different iterations of the CVM to one another and validate them against the empirically predicted peak ground motions from the 2014 NGA-West2 ground motion models. The results from this work provide a framework for updated seismic hazard analysis and direct earthquake simulation in the Pacific Northwest.

Additional Authors

Session: Fault Damage Zones: What We Know and Do Not II

Type: Oral

Room: Grand A

Date: 4/20/2022

Presentation Time: 05:30 PM Pacific

Presenting Author: Alba M. Rodriguez Padilla

Description

Measurements of the cumulative deformation history of a fault are challenged by incomplete knowledge of pre-faulted markers, sparse data coverage and limited chronologies. Using recently collected high-resolution lidar data of the Volcanic Tablelands in California, we image and analyze zones of permanent deformation associated with flexure of the hanging wall and footwall of normal faults cutting through the Bishop Tuff. High strains are localized to narrow symmetric zones (50-300 m) surrounding faults. These zones have average bending strains of ~10^-2 and exhibit constant width along most of the fault length, narrowing at the fault tips. The extent of off-fault deformation is independent of the thickness of the faulted unit, which decreases from ~100 m to ~60 m from east to west. Instead, the width of high-intensity off-fault deformation scales with fault throw following a power-law. Our observations suggest that the extent of off-fault flexural folding is rheologically controlled and directly constrains the area of influence of off-fault plastic processes.

Additional Authors

Session: New Developments in Physics- and Statistics-based Earthquake Forecasting I

Type: Oral

Room: Grand B

Date: 4/22/2022

Presentation Time: 08:15 AM Pacific

Presenting Author: Jonas Köhler

Description

The b-value from the Gutenberg-Richter relation captures the ratio between small and large earthquakes triggering for a region. Several researchers have observed fluctuation in b-values prior to an earthquake especially during the aftershock sequence analysis. By leveraging the ever-increasing earthquake database and the development in the field of deep learning computations, this study focuses on analyzing the spatial-temporal b-value series for Japan.

We follow a two step approach, in the first step a spatial-temporal b-value series is calculated from the earthquake catalog, which takes the shape of a series of [32 × 32] pixel images of spatial b-value distributions. On this we train an autoencoder, which compresses and then decompresses the input to learn the normal behavior and relationships within the data. In the second step, we then take the pixel by pixel reconstruction error as input for a Dilated ResNet-like classifier, which predicts an earthquake probability. We expect that this study will improve the understanding of earthquake occurrences which could further be beneficial for Early Warning, rapid response and mitigation plans, especially for sustainable human habitats in earthquake-prone regions.

Additional Authors

Session: Machine Learning Techniques for Sparse Regional and Teleseismic Monitoring I

Type: Oral

Room: Regency E-G

Date: 4/21/2022

Presentation Time: 08:30 AM Pacific

Presenting Author: Delaine Reiter

Description

The Air Force Research Laboratory (AFRL) initiated the Machine Intelligence for Nuclear Explosion Monitoring (MINEM) research and development (R&D) program in November 2020 with a five-year mandate to adopt machine intelligence in processing seismic and other geophysical signals to detect, locate and characterize seismic events. Automating these key processing tasks will benefit real-time monitoring operations for both earthquakes and nuclear tests.

The MINEM team includes data scientists and seismologists who are working together with AFRL and others in the U.S. Government to identify, evaluate and recommend techniques to fulfill R&D program goals. The MINEM program’s first objective involved all team members working together to identify seismic explosion monitoring processes that are amenable to machine intelligence solutions and a variety of approaches to swiftly increase automated seismic event-processing capabilities.

Seven new MINEM R&D projects are addressing various monitoring needs, including a data-sharing platform and improvements to seismic phase onset-time determination, association, amplitude measurements and event location. In this presentation, we will discuss the broad scope of MINEM, active projects and future research opportunities, with the goal of soliciting increased participation from the research community to build an R&D program that delivers more capability to the U.S. Government.

Additional Authors

Session: Advances in the Use of Seismic and Acoustic Methods to Constrain Physical Processes at Volcanoes [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/22/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: James C. Lindsey

Description

Seismicity is an an important part of volcano monitoring strategies across the globe. Seismic data from volcanic regions provides researchers with insights into the link between sub surface processes and seismicity, directly feeding back into improved monitoring and hazard assessment. Improved seismic monitoring systems that are lower power, easier to deploy and more cost effective can drive the move toward denser seismic monitoring arrays, like those outlined by the SZ4D initiative, which can more accurately characterize observed activity over time.

Güralp has addressed this issue with a sensor technology with the ability to function at any angle, without the need for a gimbal system or human interference. The Certimus broadband digital seismometer combines compact a form factor with OBS-inspired low power usage to provide the operator with easily deployable stations. An omnidirectional sensor allows the operator to install the system without levelling and without needing to intervene if the system changes orientation during deployment, e.g. during ground inflation or deflation.

A user-configurable long-period corner between 120s and 1s allows the operator to select the instrument response most suitable for the application and also eliminated the need for extensive instrument pools. All configurations can be managed on an optional hardened touchscreen locally or remotely through the web interface of the on-board Minimus digitizer. The large 64GB internal microSD cards also means that the system is well suited for offline rapid deployments.

This highly versatile and configurable sensor technology will play an important role in delivering reliable seismic data from dynamic volcanic environments, by ultimately bringing down the costs of regular sensor maintenance by reducing the need for regular sensor alignment. In addition, rapid deployment pools of seismic sensors can be streamlined as the Certimus is capable of displaying various frequency responses.

Additional Authors

Session: Fiber Optic Seismology: Understanding Earth Structure and Dynamics with Distributed Sensors [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: James T. St. Clair

Description

Distributed Acoustic Sensing (DAS), as applied in seismological investigations, measures ground motion as strain or strain-rate averaged over an interval, called the gauge length, along a cable. Traditional seismic measurements are sensitive to ground motion (e.g., velocity or acceleration) at a point rather than a spatially distributed sensitivity. To use DAS data for deriving measurements like earthquake magnitude and explosion yield estimates, using algorithms formulated for traditional ground motion measurements as inputs, it is advantageous to convert strain-based measurements into velocities or accelerations. The theoretical relationship between strain-rate and acceleration, and strain and velocity is well established and has been successfully used to convert DAS measurements in several instances, as strain-rate is proportional to acceleration and strain is proportional to velocity, where the proportionality constant is phase velocity. Strain-rate can also be derived from the spatial derivative of velocity in the direction of the fiber axis. These relationships have been used to derive several algorithms for converting DAS measurements to ground motions including spatial integration, scaling in the f-k domain and measuring moveout velocities for individual phases. While successful conversions of DAS data have been reported in the literature, difficulties have been noted in certain conditions. For example, the f-k approach can produce undesirable low-wavenumber noise, and moveout velocities derived from direct arrivals will not scale later phases correctly. Here we explore how conditions, such as geologic setting and proximity to an explosive source, may complicate relating DAS and traditional seismic measurements by comparing the performance of some of these approaches on synthetic and real DAS data.

Additional Authors

Session: Frontiers in Earthquake and Tsunami Science - Model Integration, Recent Advances, Ongoing Questions [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/22/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Tina Dura

Description

Comparison of microfossil assemblages (e.g., diatoms and foraminifera) in pre- and post-earthquake intertidal sediment is the most widely applicable and precise means to measure coseismic subsidence during past plate-boundary earthquakes at subduction zones in temperate regions. Coseismic subsidence estimates derived from transfer functions—which use the empirical relationship between modern microfossil assemblages and elevation within the tidal frame—are critical input to earthquake and tsunami source models, especially at subduction zones like Cascadia that lack historically recorded great megathrust earthquakes (M_w8+). However, differences in uncertainties on subsidence estimates between diatoms and foraminifera have not been fully explored. For example, ecological processes affect different microfossil groups in different ways, such as differing reproductive rates, sediment mixing, dissolution, limited supratidal and subtidal range. To evaluate the potential impact of these and other processes on coseismic subsidence estimates, we will compare foraminiferal- and diatom-based transfer function estimates of coseismic subsidence during the ~M9 1700 CE earthquake at a series of sites along the Oregon coast. We will develop a diatom-based Bayesian transfer function (BTF) using a new modern dataset of >150 diatom samples from transects spanning the supratidal to subtidal zones of tidal wetlands along the Oregon and northern California coasts. We will then test the performance of the BTF on a sediment contact recording a known increase in sea-level rise (equivalent to ~1m of coseismic subsidence, as might occur during a ~Mw 8-9 earthquake) from a dike removal during restoration of a former salt marsh along the Coquille River in southern Oregon. Finally, we will apply our diatom-based BTF to the 1700 CE earthquake contact at Oregon coastal sites with foraminiferal-based BTF subsidence estimates. These results will help in evaluating past and future diatom- and foraminiferal-based estimates of subsidence, and their uncertainties, during past megathrust earthquakes.

Additional Authors

Session: Tectonics and Seismicity of Intraplate Regions [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Lee Liberty

Description

We explore spatial and temporal aftershock patterns related to three instrumentally recorded earthquakes within Idaho. Bordering the eastern extent of the Snake River Plain, within the Intermountain Seismic Belt of Idaho, we compare aftershock sequences related to the Sulphur Peak, Challis and Stanley earthquakes. Using machine learning we are able to locate low magnitude events; therefore providing a robust temporal distribution of the aftershock sequence for each earthquake. To assist hypocenter location we test a range of velocity models and the AK-135 model to determine the best hypocenter locations and lowest misfit. We increased the number of detected events from: 1,946 to 74,000 for Stanley, 189 to 7,079 for Challis and 551 to 2,916 for Sulphur Peak. Early aftershock analysis for Stanley suggests that the extent of the Sawtooth Fault may extend farther than what is currently mapped, as results show a migration of events to the North-West extent of the current fault accompanied by a change from an east to west dip direction. The Challis sequence suggests similar preliminary results to the work of others, results that show a slight migration of event locations to the east and an increase in the average depth of events when compared to the USGS catalog. Preliminary results for Sulphur Peak show an increase in depth, with a mean depth of 6.4 km, as well as a migration of events to the north-west and south-east from the mainshock, intersecting the East-Bear lake normal-fault. Using machine learning picks and the localized velocity models we were able to determine the depth of the brittle-to-ductile transition zone and note that the seismogenic zone for Sulphur Peak is found approximately ~5km< the depth of the seismogenic zone for Stanley. Parameterizing the machine learning algorithm to work on a regional scale enhances seismic detection and aids our efforts in determining the driving mechanisms responsible for these three significant seismic events.

Additional Authors

Session: Searching for Fault Creep Over a Range of Timescales [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Felix Waldhauser

Description

Repeating earthquakes, earthquakes that rupture the same fault patch more than once, are playing an important role in the study of source processes and fault behavior and have the potential to improve hazard assessment and earthquake forecast. They are believed to represent brittle failure of a stuck patch (asperity) on an otherwise creeping fault, and as such may offer insight into slip behavior at depth. We present a new catalog of repeating earthquakes for northern California developed by a systematic analysis of the entire NCSN waveform archive between 1984 and 2014 to identify earthquakes that are co-located, are of similar size and share similar waveforms. We find 27,675 events in 7,713 repeating earthquake sequences (RES) that include between 2 and 32 events with magnitudes between -0.5 and 6.5. Temporal behavior of the events within each RES ranges between random and quasi-periodic over the 30-year observation period and includes temporal clustering (bursts). The RESs occur throughout northern California, with some of the largest and most periodic sequences predominately, but not exclusively, along faults within the San Andreas Fault system that exhibit surface creep. Piecewise periodic RESs are found near large earthquakes where they are modulated by transient stress. Slip rates inferred from the new data, while generally consistent with published estimates from geodetic and surface data, offer a high-resolution image of subsurface creep along individual fault strands and resolve slip partitioning across wider zones of deformation. The new repeater catalog forms the baseline for routine detection and analysis of repeating events in real-time to help monitor changes in fault properties and loading rates.

Additional Authors

Session: Tectonics and Seismicity of Intraplate Regions I

Type: Oral

Room: Cedar

Date: 4/20/2022

Presentation Time: 09:00 AM Pacific

Presenting Author: Tim F. Redfield

Description

We present a conceptual seismological model for Fennoscadia that is consistent with modern hypotheses of extended margin evolution, including post-breakup reactivation by footwall uplift in regions adjacent to sharp crustal taper. Fennoscandia’s seismicity reflects the benchmark domain boundaries of its Mesozoic rifted margin: Three distinct belts of earthquakes strike sub-parallel to the generalized line of breakup. The outermost seismic belt marks the Taper Break (TB), or the zone of flexural coupling/decoupling between the distal (seaward) and proximal/necking (landward) domains. A coastal belt follows the Innermost Limit of Extension, defined as the onset of 39 km-thick crystalline continental crust. An interior belt follows the landward limit of the Scandinavian uplift. Between each belt, large portions of the necking, proximal and hinterland domains are seismically quiescent.

As proposed by previous authors, a first-order spatial correlation between Scandinavia’s offshore earthquake belt and voluminous, geologically rapid, Neogene sedimentary loading is evident. However, the presence of thinned, faulted crystalline basement is also a very important factor behind Scandinavia’s offshore seismicity. Where the Neogene deposits are thickest the underlying crust is oceanic; released energy is lower per unit area there than where lesser Plio–Pleistocene loading impacts continental crust that was fully prepared by necking and hyperextension. These data suggest that the ‘strength’ of the TB and the continental margin’s distal domain is significantly less than that of relatively young (ca. 54 Ma) oceanic lithosphere. Our data also imply that ridge push does not contribute significantly to Fennoscandia’s seismicity. Rather, we find that thin-plate bending stresses stemming from offshore depositional loading conspire with unbuttressed Gravitational Potential Energy (GPE), onshore erosion and post-glacial isostatic rebound to generate Fennoscandia’s earthquakes.

Additional Authors

Session: Using Data and Experience to Improve Geohazards Communication

Type: Oral

Room: Grand B

Date: 4/20/2022

Presentation Time: 02:30 PM Pacific

Presenting Author: Nathan C. Becker

Description

As part of its outreach efforts toward mitigating tsunami hazards, the Pacific Tsunami Warning Center (PTWC) began posting computer animations to its first official social media site, it’s Facebook Page, in August of 2012. Nearly a year later, in June of 2013, PTWC also gained a YouTube channel and has been posting new content there ever since. PTWC produced its initial video content for these sites by adapting the data visualizations it had previously generated for a NOAA Science-on-a-Sphere (SOS) exhibit at Honolulu’s Bishop Museum. PTWC had originally adapted these SOS visualizations from the map displays it developed for its tsunami warning operations showing historic earthquake and tsunami activity and of tsunami forecast model output. Through 2015 PTWC experimented with display style while releasing new animations on the anniversaries of significant historic tsunamis and for Tsunami Awareness Month in Hawaiʻi. At the same time PTWC continued to develop its animation code, ultimately leading to real-time wave-propagation animations for both YouTube and SOS. Through collaboration with an outreach specialist and with feedback from colleagues and test audiences PTWC then created a standardized set of animations of historic tsunamis and global earthquake activity for both YouTube and SOS, and again released individual animations to the public on significant anniversaries over 2016-2017. From 2018 through 2020 events prompted the creation of animations focused on seismic activity at local and regional scales for Kīlauea Volcano, Puerto Rico, and California. Since then PTWC has continued to innovate with new animations for recent and historic events such as three simultaneous tsunamis in 2021 and a 120-year sequence of historic earthquakes and tsunamis. Links: https://www.youtube.com/user/PacificTWC; https://sos.noaa.gov/.

Additional Authors

Session: Structure and Seismogenesis of Subducting Slabs [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/22/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Zhichao Shen

Description

The intermediate- (10-100 km) and small-scale (<10 km) slab structures below 410 km are important manifestations of various thermal and petrological processes. However, seismic imaging of these structures has been particularly challenging because the seismograms recorded on the surface can be easily complicated by shallow structures. To resolve the subtle seismic signatures from deep slabs without influence from shallow complexities, we apply a novel inter-source interferometry method that turns deep earthquakes into virtual seismometers closer to the target. Using data from Hi-net, we not only present strong evidence for an intermediate-scale metastable olivine wedge and small-scale intra-slab heterogeneity beneath the Japan Sea, but also constrain their dimensions and velocity perturbations more accurately than before. The results suggest that the initiation mechanism of deep earthquakes is due to transformational faulting of metastable olivine, while revealing petrologic processes associated with dehydration of subducting slabs. Beyond the relatively independent scales of slab structures and dynamics, our findings point toward a consistent picture of a dry slab core below 410 km beneath the Japan Sea.

Additional Authors

Session: Improving Strong-motion Data, Products and Services: From Waveform Quality to Open Dissemination [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Chunyang Ji

Description

This work presents a ground motion database for California and its close surroundings (i.e., areas near the border with Nevada, Oregon and Arizona) between 1999 and 2021 observed by 74 different networks and data centers. This DesignSafe ground motion database for California is hereafter referred to as the DSGM-CA and is available at DesignSafe-Ci. The DSGM-CA includes earthquakes with magnitudes larger than 3 and focal depths less than 40 km. Ground motion records and events included in this dataset are collected and processed using the gmprocess toolkit, which is an automated protocol developed by the USGS. Path measures such as rupture distance and epicentral distance are computed. Pseudo-Spectral accelerations, duration metrics, Arias intensity and other ground motion intensity measures are provided for records that pass the quality assurance (e.g., signal-to-noise check) check performed by the gmprocess toolkit. Additionally, site metadata are provided, including wave velocity information (from proxy-based time-averaged shear-wave velocity for the top 30 m, V_s30, and from P- and S- wave measured velocity profiles when available), predominant frequency measured from microtremor-based horizontal-to-vertical ratios and site-specific kappa0 values computed from multiple ground motions recorded at each station. 131651 ground motions observed from 1251 earthquakes are included in this database with distances ranging from 0.24 to 335 km, which are accessible via DesignSafe.

Additional Authors

Session: Everything Old Is New Again – Resurging Use of Analog Data [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Lorraine J. Hwang

Description

Legacy seismic data is an important primary data set of observations of seismic events that occurred in the past century. Using new methods and applying new insights and discoveries, careful reuse of these data has furthered our understanding of seismogenic processes. However, much of this data remains undiscoverable to a generation of digital seismologist. Accessing physical seismograms from collections often requires retrieval from hard to access facilities. In recent years, recognition of the fragile state of many collections and the emphasis on FAIR data has led to a renewal in efforts to preserve these collections digitally for future use. Efforts are underway to establish minimal metadata and best practices for the preservation of these growing collections. However, to be FAIR, the data not only need to be open licensed and available, they must also be discoverable.

To aid researchers in the discovery of legacy seismic data, we have created a directory that provides information about available resources. The goal is to assist in the discovery and access of legacy seismic data collections worldwide. Legacy seismic data is any data related to the operation of seismic networks that were not collected originally in digital form. This includes seismograms, station bulletins, phase cards, among other artifacts. The initial stage of the project focuses on seismogram collections originally recorded on paper but can include data recorded on other media such as FM tape. We present information from publicly available sources about seismograms that are available in digital format typically as digital images. Interactive maps show available data by station, event, and managing organization and provide a starting point to access additional information on the resource as well as references in the literature. In building a community for FAIR legacy data, we seek contributions and feedback in developing this open-source project as a valued community-maintained resource.

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Session: Numerical Modeling in Seismology: Developments and Applications I

Type: Oral

Room: Regency A-C

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Alice-Agnes Gabriel

Description

Simulations of sequences of earthquakes and aseismic slip (SEAS) including more than one fault and complex geometries are challenging. We present a symmetric interior penalty discontinuous Galerkin (SIPG) method accounting for the complex geometries and heterogeneity of the subsurface. The method accommodates two- and three-dimensional domains, is of arbitrary order, handles sub-element variations in material properties and supports isoparametric elements, i.e. high-order representations of the exterior and interior boundaries and interfaces including intersecting faults. We provide an open-source reference implementation, Tandem, that utilises highly efficient kernels, is inherently parallel and well suited to perform high resolution simulations on large scale distributed memory architectures. Further flexibility is provided by optionally defining the displacement evaluation via a discrete Green's function, using algorithmically optimal and scalable sparse parallel solvers and preconditioners.

We highlight the characteristics of the SIPG formulation via an extensive suite of verification problems (analytic, manufactured and code comparison) for elasto-static and seismic cycle problems. We demonstrate that high-order convergence of the discrete solution can be achieved in space and time for elasto-static and SEAS problems. Lastly, we apply the method to realistic demonstration models consisting of a 2D SEAS multi-fault scenario on a shallowly-dipping normal fault with four curved splay faults and a 3D multi-fault scenario of instantaneous displacement due to the 2019 Ridgecrest, CA, earthquake sequence. We exploit the curvilinear geometry representation in both application examples and elucidate the importance of accurate stresses (or displacement gradients) representations on-fault. Our results exploit advantages of both the boundary integral and volumetric methods and is an interesting avenue to pursue in the future for extreme scale 3D SEAS simulations.

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Session: Earthquake Source Processes at Various Scales: Theory and Observations [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Giovanna Calderoni

Description

We present a new approach aimed to generalize the statistical procedure proposed by Calderoni et al., (2017) to estimate the prevailing direction of rupture propagation in a given region during a seismic sequence. We apply this procedure to the strongest earthquakes (Mw ≥ 4.4) of the 2016-2017 Central Italy seismic sequence and compare our results with other studies.The method is based on the Empirical Green Function (EGF) deconvolution method. The main advantage of our method is that it is conceptually simple and fast (near real-time speeds) and can be applied to any active seismic area. Results show heterogeneity of rupture directivity along the activated fault system with a complex pattern even if most of the studied events have similar focal mechanisms. However, homogeneous pattern in rupture directivity is observed along the activated fault system and the preferred trend of the rupture propagation is in large part controlled by pre-existing structural discontinuities, i.e., the NW-SE faults. Therefore, we suggest that pre-existing structural discontinuities may control the directivity in the way that such discontinuities represent weakness zone, i.e., zones affected by a bi-material fault interface. We also discuss the possible role of fluids as a cause of bi-material and propose an interpretation of our results based on the role of fluids in the studied sequence as reported in literature.

Furthermore, we investigated a possible control of rupture directivity on the location of immediate aftershocks. We calculated the cumulative number of events, which occurred in the forward, backward and orthogonal rupture propagation direction, before and after the occurrence of events and found that for the analyzed events immediate seismicity mainly appears to be correlated with rupture directivity along the pre-existing structural discontinuities.

Additional Authors

Session: Modeling, Collecting and Communicating Post-earthquake Hazard and Impact Information [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Christina Sanon

Description

In the aftermath of an earthquake, data collection is an important part of the response and is used for both loss assessment and data curation for model development. For liquefaction impacts, post-earthquake data collection often relies on field investigations, which are usually spatially limited and incomplete. Field investigations may capture liquefaction spatial extent and resulting deformations, but not consistently. With the increased availability of high-resolution optical imagery and radar technologies like Synthetic Aperture Radar (SAR), researchers in recent years have employed a combination of field surveys and visual and automated mapping of liquefaction surface effects using remotely sensed data sources. The inconsistencies in how the field investigations and remotely sensed observations are mapped can impede liquefaction inventory development, in part due to the range in size of liquefaction features (cm’s to 10s of m’s) and the inconsistency of feature attributes. Prior liquefaction inventories are point-based and summarize liquefaction occurrence across a site (10s of m) as a single point and as a binary variable: liquefaction occurrence vs. non-occurrence. Visual assessment of surface effects and detailed spatial mapping demonstrate that not all liquefaction features are equivalent and liquefaction inventories would benefit from a measure of size as well as deformation. In this study, we provide a liquefaction image library that includes spatial polygons and labels for over 2000 liquefaction features with information such as the infrastructure impacted and the size of the features across multiple events: including significant liquefaction events such as Christchurch (2011) and Tohoku (2011), as well as minor liquefaction events such as Haiti (2010) and Puerto Rico (2020). Our study proposes a methodology and establishes an image-based liquefaction inventory using remotely sensed data like optical and SAR imagery that not only provides occurrence and non-occurrence labels, but also provides information on impact in terms of feature size, impacted infrastructure and deformation.

Additional Authors

Session: Advances in Earthquake Early Warning: Research, Development, Current State of Practice and Social Science I

Type: Oral

Room: Cedar

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Alexander Fozkos

Description

The goal of this study is to provide initial considerations for early warning tailored to the tectonics Alaska.

Active tectonics between the Pacfic and North American plates make Alaska one of the most seismically active areas in the world. While many of the large earthquakes in Alaska happen offshore, along the Aleutian Islands, events also occur inland at deep tectonic interfaces and numerous fault systems in the crust. These earthquakes pose serious hazards. History demonstrates this clearly. Implementing an earthquake early warning system tailored for Alaska's unique seismic setting is an inevitable development both through corporate entities and as an extension of the current early warning systems along the US west coast.

We use a scenario-based approach to examine the trade-offs between ground motion and initial warning time for a variety of realistic earthquakes. Our warning time estimates are derived from the current network of seismic stations and simple traveltime estimates. We use ShakeMap to forward model the ground motions. We present relationships between warning time, intensity of shaking and different earthquake characteristics, such as depth, magnitude, location and proximity to significant population. These findings illustrate the types of scenarios that should be addressed as we begin to consider what early warning in Alaska might look like.

Additional Authors

Session: Fault Damage Zones: What We Know and Do Not II

Type: Oral

Room: Grand A

Date: 4/20/2022

Presentation Time: 05:00 PM Pacific

Presenting Author: Xiaohua Xu

Description

Seismic velocities are known to reduce around the vicinity of a fault. This reduction is often characterized by the existence of a fault damage zone, the structure and property of which, indicate the maturity of the fault and affect future co-seismic rupture process. There has been lots of seismologic studies that reported such reduction and vp/vs ratio changes along many faults. Here we present a geodetic approach on constraining the structure and velocity changes in fault damage zones. When earthquake stress release causes compliant deformation on its nearby faults, one could detect these motions with high-resolution InSAR acquisitions. With the deformation profiles, the width of the fault damage zones could be directly measured. Using a fault slip model, we could then estimate the strain conditions across these compliant faults. We input these into a finite element fault zone model to fit the fault-parallel and vertical deformation profile by changing the depth extent of the damage zone, its shear modulus reduction and Poisson’s ratio. The depth extent is constrained by the decay of the deformation profile outside of the damage zone, while the horizontal amplitude is controled by the shear modulus reduction. Given these two parameters, one could further change the p-wave velocity to get the right amplitude for vertical deformation. Compared to seismic analysis that is usually limited by the resolution, this geodetic approach is mostly definitive.

Additional Authors

Session: Advances in Geospatial Modeling of Seismic Hazards

Type: Oral

Room: Grand C

Date: 4/20/2022

Presentation Time: 02:45 PM Pacific

Presenting Author: Weiwei Zhan

Description

One-dimensional (1D) site response models assume vertically incident SH waves propagating through laterally constant soil layers. These assumptions, collectively referred to as the SH1D model, are widely used in site-specific ground motion predictions, although many studies have demonstrated their limitations. The term “site response complexity” (SRC) refers to the degree of discrepancy between the observed empirical transfer function (ETF) and the theoretical transfer function (TTF) computed with SH1D modeling. We present a geospatial approach to estimate site response complexity using statistical and machine learning methods with globally or regionally available geospatial proxies. Our site response data are from 114 vertical seismometer arrays in Japan’s Kiban-Kyoshin network (KiK-net) used in Kaklamanos and Bradley (2018). The SRC data are calibrated according to the Thompson et al. (2012) taxonomy that relies on two parameters, r (Pearson’s correlation coefficient between the ETF and TTF) and σ_i (inter-event variability of the ETF). We examine 18 geospatial proxies associated with site stiffness, topography, basin and saturation conditions. Using the geospatial proxies as explanatory variables, two sets of predictive models are developed: (a) linear regression models for predicting r and σi, separately; and (b) multiclass classification models for site response complexity. Our optimal SRC classification model uses the slope-based average shear wave velocity (V_S30), global sedimentary deposit thickness, depth to shear wave velocity of 1.5 km/s (Z_1.5) and global water table depth as explanatory variables. We generate maps across Japan for r, σ_i and SRC class, which can provide first-order approximations of site response complexity and exhibit clear patterns between SRC class and topography. LG sites are mostly located in flat sedimentary basins, LP sites are often located near mountain/basin edges, and H sites are located within mountainous areas. We conclude that a geospatial model for site response complexity is a promising first-order estimate of complexity in site response across broad regions.

Additional Authors

Session: 50-State Update of the USGS National Seismic Hazard Models III

Type: Oral

Room: Regency E-G

Date: 4/20/2022

Presentation Time: 02:45 PM Pacific

Presenting Author: Zoya Farajpour

Description

We developed a new ground motion model (GMM) for predicting ground shaking of future induced earthquake events in Central and Eastern United States. The new model is a new empirical-hybrid ground motion model (GMM) for small-to-moderate potentially induced earthquakes for Central and Eastern United States (CEUS). For this study, Pezeshk et al.'s (2018) model was used as the base model which was developed and calibrated for tectonic events in Central and Eastern North America (CENA) as part of the Next-Generation Attenuation-East (NGA-East) project. The model is a calibrated version of the base model by using a comprehensive database of potentially induced ground motions with a smaller range of magnitudes and depths than tectonic earthquakes. We implement a compiled dataset containing more than 31,000 strong-motion records from 2,596 earthquake events recorded at 370 stations. The Gulf Coast region’s all earthquake events and stations are excluded from the database of this study.

The functional form of the developed model includes 5 coefficients are extracted by using a mixed-effect regression algorithm. The proposed GMM is derived for the peak ground acceleration and response-spectral ordinates at periods ranging from 0.01 to 10.0 sec, magnitudes ranging from 3.0 to 5.8 and hypocentral distances up to 200 km. The proposed GMM has applicability in long-term and short-term U.S. Geological Survey National Seismic Hazard Maps and for the hazard evaluation of induced seismicity. We also assessed the performance and predictive capability of the developed GMM through a set of comprehensive residual analyses and compared the proposed GMM with five recently developed GMMs for earthquakes in CENA. The GMMs are utilized in the PSHA assessment of induced earthquakes through the observed data for CEUS.

Additional Authors

Session: Development, Enhancement and Validation of Seismic Velocity Models [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Debajeet Barman

Description

Determining the structural relationship between the Suwannee and its adjacent terranes on the margin of Laurentia is critical to understanding the formation of Laurentia and the tectonics of the Alleghenian orogeny. Previous studies demonstrated that the formation of the passive continental margin resulted from the movement of Laurentia towards the west-northwest during Proterozoic rifting. In our study there are two primary goals: 1) create high-resolution velocity maps to accurately quantify the extent of the terrane boundaries, 2) estimate the potential of the Non-linear Signal Comparison method in improving the phase velocity estimates using ambient noise data.

We use vertical-component ambient noise data from 100 broadband seismic stations (EarthScope FlexArray project called SESAME (Z9 2010-14; Parker, 2015)). Several approximately linear array subsets are used to obtain Green’s function. Then the phase velocities between two stations are estimated using Non-Linear Signal Comparison (NLSC; Zheng and Hu, 2017). This method mitigates the non-uniqueness problem at deeper depths. Phase velocities are estimated for Rayleigh waves at periods (15-45s) to obtain phase velocity dispersion curves. These dispersion curves are inverted to obtain 1D shear wave velocity profiles at locations along a transect; these profiles are then interpolated to produce 2D models.

NLSC improves the accuracy of Green’s functions, particularly at longer periods, by reducing the uncertainties of phase velocity estimates in dispersion curves at lower frequencies. Here, the time lag between two Green’s functions is not used directly. Instead, the exponent of the time lag is used and the normalized dispersion spectrum is calculated to estimate the dispersion curve. Dispersion curves are used to model the shear wave velocity using a Bayesian approach (Markov Chain Monte Carlo), which provides the maximum likelihood estimate of shear wave velocity. Results using real data show significant improvement in the estimation of Rayleigh wave phase velocity, particularly in the lower crust and uppermost mantle, compared to conventional techniques.

Additional Authors

Session: Development, Enhancement and Validation of Seismic Velocity Models

Type: Oral

Room: Grand C

Date: 4/21/2022

Presentation Time: 05:15 PM Pacific

Presenting Author: Afifa Imtiaz

Description

Local shear-wave velocity (Vs) structure and sedimentary thickness are considered to be the controlling parameters in seismic amplification. Using dispersion characteristics of surface waves from ambient vibration array data has proven to be an effective tool for imaging subsurface Vs profiles. However, the conventional optimization inversion techniques are limited in their ability to account for the inherent non-uniqueness of this inverse problem and related uncertainty of the profiles. Therefore, we apply a novel Bayesian inversion approach based on a Multizonal Transdimensional Inversion (MTI) with the aim of developing a 3D Vs model for Basel, Switzerland. It is based on a joint inversion of multimodal Rayleigh- and Love-wave dispersion curves (DCs) along with Rayleigh-wave ellipticity. The key advantages of the MTI are that the number of layers is determined self-adaptively from the measured data and model uncertainties can be assessed quantitatively. Moreover, the solution of the Bayesian inversion is the posterior Probability Density Function that results from prior expectations and observed data supplemented by an expected distribution of data errors. Hence, the model uncertainty can be duly propagated from DCs to Vs profiles.

We apply MTI to retrieve 1D Vs profiles from 32 passive arrays located within about 130 sq. km area by using single-zone transdimensional model space with homogeneous prior assumptions. It delivered a major improvement in our results because such joint inversions of surface wave dispersion and ellipticity curves could be performed only for a few sites in Basel in the past. Mulitizonal inversion is performed by drawing additional constraints on depths of intermediate layers from a rigorous 3D geological model. The results are promising in better resolving the interfaces corresponding to major velocity contrasts and the rate of Vs change with depth, especially in the complex sedimentary structure of the Rhine Graben formation.

Additional Authors

Session: Things That Go Bump: Identifying and Characterizing Non-Earthquake Seismo-Acoustic Sources [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/20/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Kate E. Allstadt

Description

We present an update to the collection of seismogenic mass movements that forms the basis of the Exotic Seismic Events Catalog (ESEC), doubling the number of events in the catalog from 121 to 242 while broadening the geographic distribution and range of event types. The ESEC is available online through IRIS’s searchable product depository or as a downloadable SQLite database from USGS ScienceBase. This update adds more instances of seismogenic landslides, debris flows, snow avalanches, outburst floods and lahars as well as some new event types: two mine collapses, a submarine landslide and a volcanic flank collapse. We also now incorporate infrasound detection. Whereas the first version of the catalog focused on mass movements located primarily in the Western United States and Canada, this update includes events from Europe and Pacific Islands. We only include events for which seismic data are openly available.

We provide both basic seismic information (e.g., station detections on different frequency bands, seismic data location, etc.) and ancillary data such as geometric measurements, references, photographs and satellite imagery. When available we use published values such as source location, drop height, runout distance and volume, and when not documented, we estimate values from satellite imagery or photographs. Events are categorized in terms of the quality of the ancillary data, and we provide estimates of uncertainty on parameters such as location and volume. This update increases the availability of seismogenic mass movement data to the community to promote research that betters our understanding of event dynamics and improves methods for exotic event detection, classification, and characterization. Future updates could allow for the incorporation of other exotic event types like blasts and glacial events. The ESEC has a mechanism for community members to contribute events to the collection, so we encourage other researchers to join in the effort.

Additional Authors