Session: Special Applications in Seismology - I

Type: Oral

Room: Tubughnenq’ 3

Date: 5/1/2024

Presentation Time: 05:00 PM Pacific

Presenting Author: Santiago Rabade

Description

The #Utequake project is an outreach initiative from the University of Utah Seismograph Stations that bridges the gap between science and Athletics. For this project, we deployed a strong motion station in Rice-Eccles Stadium to record and correlate in real-time the signals generated by the crowd during University of Utah football home games. In this work, we showcase the visibility and impact of the project on social media, the University, and local media, and we will show some comparisons of the largest amplitude signals during the 2023 season. #Utequake showcases the powerful intersection of science and sports, creating a platform for education, entertainment, and community engagement.

Additional Authors

Session: Detecting, Characterizing and Monitoring Mass Movements [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/2/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Liam D. Toney

Description

It is well known that surficial mass movements (SMMs), such as landslides and rock falls, have seismic signatures distinct from other routinely-recorded seismic sources like earthquakes and explosions. However, overlaps between the characteristics of these signals can still make it difficult to discriminate between source types during operational seismic monitoring. This ambiguity motivates the development of automated techniques for seismic signal classification. Furthermore, seismic differentiation within the broad class of SMMs has additional scientific and rapid response value. Examination of SMM seismic waveforms highlights a particularly strong contrast between the signals produced by primarily vertical processes — i.e., "falls" — versus processes that have a non-negligible horizontal component — e.g., landslides and avalanches, or "slides" in our abbreviated terminology.

Here, we present a machine learning (ML) classification scheme for differentiating between seismic signals generated by falls versus slides. We additionally include shallow earthquakes and blasts because these are most similar to SMM signals and are commonly recorded on regional seismic networks. These classes, therefore, are the most useful for automated classification. We neglect debris flows in this study because of their much longer durations and low amplitudes. Our signals derive from waveform picks in the Exotic Seismic Events Catalog, a diverse collection of non-earthquake seismogenic surface events, and the ANSS Comprehensive Earthquake Catalog. We use a shallow, feature-based approach to classification using statistical metrics extracted from waveforms. Feature importance metrics provide insight into the ML methods we use, which leverage both unsupervised techniques (to assess the diversity of seismic signals in our training dataset via clustering) and supervised techniques (to train and evaluate a classifier). We picture our classification workflow as one modular element of a larger non-earthquake assessment workflow that includes detection and location as preliminary (or concurrent) steps.

Additional Authors

Session: Earth’s Structure from the Crust to the Core - III

Type: Oral

Room: Tikahtnu Ballroom E/F

Date: 5/1/2024

Presentation Time: 03:00 PM Pacific

Presenting Author: Philippe H. Lognonné

Description

The Mars NASA InSight mission re-started seismology in planetary science, 40 years after Apollo and Viking.

SEIS, InSight’s French led international seismometer, operated from 2/2019 to 12/2022. Thanks to its ground installation and wind shielding, the very-broad-band (VBB) sensors of SEIS achieved ultra-low noise levels during the first half of the night. This enabled a very low detection threshold, down to moment magnitude M_W=1 regionally and 4 on a global scale.

More than 1300 events during the 4 years of operation were detected by the MarsQuake Service from VBB data, including a M_W =4.7 marsquake that excited surface waves and likely normal modes. Eight impacts were also confirmed by orbital crater imaging, two with M_W =4 and very large craters. Nearly half of the events were located near Cerberus Fossae, where possibly volcanic seismo-tectonics is ongoing.

Through these seismic events, SEIS provided the first seismic models of Mars, from the 40 km thick crust beneath InSight down to the core. These models revealed the stratigraphy of the crust, including through surface wave anisotropy, the structure and thickness of the thermal lithosphere and the presence of a molten silicate layer at the bottom of the mantle beneath a partially molten layer. Comparisons of these Martian interior and seismic properties with those of the Moon and Earth, obtained from Apollo and Earth seismic networks, are now possible, opening a new research field: comparative planetary seismology

And SEIS will continue its journey to the Moon with the JPL/CNES/IPGP Farside Seismic Suite, which will deploy in 2026 one of the spare sensors of InSight VBBs in the farside Schrödinger basin. FSS will operate this vertical VBB with performance at 1 Hz more than 10x better the Apollo seismometers. Data will be processed by the FSS LunarQuake Service and will be completed by Earth based impact flash monitoring. We therefore conclude with the science goals of this new mission in terms of deep interior imaging, as well as perspectives in terms of global seismic network on the Moon, if complemented by other missions deploying seismometers.

Additional Authors

Session: Illuminating Complex, Multiplet Earthquake Sequences at Kahramanmaras (Turkiye), Herat (Afghanistan), and Beyond - II

Type: Oral

Room: Kahtnu 1

Date: 5/2/2024

Presentation Time: 11:30 AM Pacific

Presenting Author: Margaret Hellweg

Description

The Mendocino Triple Junction (MTJ), north of 40N and west of 122W, is one of California’s tectonically most active and complex regions. Two earthquake sequences in the MTJ region, beginning on 2021-12-20 (2021) and 2022-12-20 (2022), respectively, highlight the faults in the Gorda plate as it subducts beneath the North American plate. Upgrades to the instrumentation in the region in recent years allow a detailed exploration of the seismicity and finite faulting associated with these earthquakes, in order to better define the faults within the subducting Gorda plate, as well as their modes of rupture. The December 2021 sequence began with a doublet, separated by ~11 s in time and 30 km in space. Detailed analysis indicates that the first event was offshore (2021-OFF) on the Mendocino fault (MF) between the Pacific and Gorda plates. The second event was onshore (2021-ON) at a depth of 24 km within the subducting Gorda plate and was most likely triggered by the S-waves of 2021-OFF. Simultaneous finite source modeling of the two events indicates that they have about the same magnitude, M~6.1, despite the waveforms of 2021-OFF appearing smaller in recordings because it was more distant from all recording stations which are onshore. The source analysis shows that 2021-OFF ruptured eastward along the MF, and 2021-ON ruptured to the NE. The 2022 sequence began with a mainshock (2022-MS, M6.4) just off Cape Mendocino to the NW of 2021-ON, also on a fault within the Gorda plate. Its largest aftershock (2022-AS, M5.4) took place 11 days later about 40 km to the ESE of the main fault rupture. Finite source analysis of 2022-MS indicates that it ruptured NE, toward the towns in the area and caused damage exacerbated by 2022-AS.

Additional Authors

Session: Advancing Seismology with Distributed Fiber Optic Sensing [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Walid Ben Mansour

Description

Ambient noise tomography is a well-established technique that estimates the physical properties (i.e., thickness and shear-wave velocity) of the crust and upper mantle through the inversion of surface-wave dispersion curves. Imaging the shallow crust and sediment layers can be difficult, especially offshore, due to the limited number of ocean bottom seismometers. A more accurate sediment mapping on the continental shelf can help identify potential risks like underwater landslides that could damage telecommunication cables or trigger tsunamis. The recent development of the Distributed Acoustic Sensing (DAS) technology presents an opportunity to achieve higher-resolution imaging of the offshore sub-surface using dense station spacing distributed along a fiber-optic cable. We probed 50 km of a telecommunication fiber deployed offshore Cordova, Southern Alaska, and recorded continuous data for four months in 2022. The sediment cover on the continental shelf is likely to have a significant portion of glacial sediments originating from the Copper River, which is situated a few miles to the south. Although no large earthquake (Mw>7.0) has occurred in the region since the 1964 M9.2 Prince William earthquake, the area remains seismically active and susceptible to underwater landslides. We use the data collected from May 04 to May 15, 2022, to compute cross-correlation functions between station pairs along the fiber. From a frequency-time analysis, we estimate surface-wave phase velocity between groups of station pairs and invert to produce a 2-D shear wave velocity profile. In this work, we propose to use a Bayesian Monte Carlo inversion framework to build our final velocity profile. The inverted shallow velocity profile provides new constraints on the nature of the sediments in this seismically active region. We will discuss the implications in terms of sediment transport and mixing but also the potential of underwater landslides associated with these sediments.

Additional Authors

Session: Physics-Based Ground Motion Modeling - I

Type: Oral

Room: Kahtnu 1

Date: 5/3/2024

Presentation Time: 08:45 AM Pacific

Presenting Author: Ke Xu

Description

The Salt Lake City Segment of the Wasatch fault (WFSLC), where the probability of a M7 earthquake in the next 100 years is estimated to be 16% (McCalpin and Nelson, 2000), is a primary seismic hazard to the Salt Lake Valley, populated by 1 million+ people. The 2020 Magna, UT, earthquake, which likely occurred on the WFSLC, generated Peak Ground Accelerations (PGAs) as large as 0.55 g, and was a stern reminder of the seismic hazards for the area. Here, we present 3D wave propagation simulations of the Magna earthquake sequence in the Wasatch Front Community Velocity Model (WFCVM, Magistrale et al., 2008) up to 10 Hz to better constrain both linear and nonlinear parameters in the soils of the Salt Lake Valley. We first validated the WFCVM via linear simulations of a M4.5 aftershock in the Magna sequence. By adding a geotechnical layer outside the basin, a statistical distribution of small-scale velocity heterogeneities with 10% standard deviation, and using frequency-dependent anelastic attenuation as Q_s=0.05*V_s (f<1 Hz) and Q_s(f)=0.05*V_s*f^0.4 (f>1 Hz, V_s in m/s), we obtained an overall satisfactory fit to the seismic recordings for the aftershock. Our simulations of the 2020 Magna main shock use finite-fault source models from the Graves-Pitarka rupture generator, and a preferred source model is chosen with minimal bias to data at f<1 Hz, where nonlinear effects are expected to be negligible. Although different plausible source realizations result in factor-of-ten variations in high-frequency synthetic ground accelerations, they generally overestimate those of the recordings, in particular at stations with the largest PGAs, suggesting the presence of nonlinear soil effects. Then, using a fully hysteretic multi-yield-surface 3D method (Roten et al., 2023) we find that Darendeli’s (2001) proposed reference strain-depth relations provide excessive damping of the high-frequency synthetics in the Magna area, with an optimal fit to observations for reference strains 3 standard deviations larger. Our findings provide a basis for improved seismic hazard analyses of the greater Salt Lake City region.

Additional Authors

Session: Seismic Monitoring, Modelling and Management Needed for Geothermal Energy and Geologic Carbon Storage - III

Type: Oral

Room: Tikahtnu Ballroom A

Date: 5/2/2024

Presentation Time: 03:00 PM Pacific

Presenting Author: Lianjie Huang

Description

Lightning Dock Geothermal (LDG), is an operating power plant in Hidalgo County, southwest New Mexico, USA. LDG LLC conducted a 3D active-source surface seismic survey in 2011 using accelerated weight drop sources for subsurface characterization. The 3D seismic survey covered a region of approximately 4 km in the east-west direction and approximately 3.5 km in the north-south direction. This 3D seismic survey used a simple square pattern to distribute source and receivers. The survey used a total of 17 receiver lines with a quasi-equal spacing of 660 ft and with an orientation of the north-south direction, and a total of 21 source lines with a quasi-equal spacing of 600 ft and with an orientation of the east-west direction. Within the source lines or the receiver lines, the source interval is 110 ft and the receiver interval is 220 ft. We perform migration velocity analysis and prestack depth migration to produce a high-resolution subsurface image, and then delineate faults on the migration image using a machine learning method. Our results provide valuable information for siting new wells to improve the geothermal energy production at the Lightning Dock geothermal area.

Additional Authors

Session: Physics-Based Ground Motion Modeling [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Anupam Patel

Description

A recurrence of the 1755 Lisbon earthquake would be devastating for present-day Portugal. However, despite widespread research into the possible sources for the event, the associated fault(s) and magnitude of the earthquake are still uncertain. Previous simulation studies have used velocity models with relatively coarse resolution (Grandin et al., 2007) or stochastic modeling techniques that exclude potentially important wave propagation effects (Carvalho et al., 2004; Carvalho, Zonno, et al., 2008). Here, we use 3D physics-based simulation in the recent PRISM3D reference model for Iberia (Arroucau et al., 2021), that we validate against data from a 2018 M4.3 earthquake near Lisbon. We obtain an optimal fit to the 0-1 Hz strong motion recordings of the validation event using a geotechnical layer with a tapering depth of 350 m, a statistical distribution of small-scale heterogeneities with a standard deviation of 5 percent, and anelastic attenuation for S-waves using Qs = 0.1Vs (Vs in m/s). We then use the validated model to simulate 0-1 Hz wave propagation for 40+ plausible earthquake scenarios across proposed fault structures. Most of the single fault sources tested for the 1755 Lisbon earthquake inadequately replicate the observed Modified Mercalli Intensity (MMI) pattern from the event, while other scenarios violate reported tsunami arrivals or ground motion durations. However, we find that a Mw8.3 scenario event on the Guadalquivir Bank Fault generates MMI patterns most comparable to the reports. Moreover, the combined wavefield from a Mw8.4 event on the Marques de Pombal Fault with that of a (possibly triggered) Mw7.75 earthquake on the Tagus Abyssal Plain fault yields a satisfactory fit to the isoseismal data from the 1755 earthquake.

Additional Authors

Session: 3D Wavefield Simulations: From Seismic Imaging to Ground Motion Modelling - I

Type: Oral

Room: K’enakatnu 6

Date: 5/2/2024

Presentation Time: 08:15 AM Pacific

Presenting Author: Audrey Dunham

Description

The Cascadia Subduction Zone (CSZ) is anomalously quiet, with a dearth of moderate-to-large magnitude seismicity in the instrumented record. However, paleoseismic evidence indicates that the CSZ ruptures in large (~M8-9) megathrust earthquakes, with the last great event occurring in 1700. To quantify the seismic hazard due to great CSZ earthquakes, we employ numerical methods to simulate ground motions of many M8.7-9.2 megathrust earthquake scenarios. Here, we present preliminary results from the next generation of 3D broadband (up to 10 Hz) ground motion simulations for the CSZ, building off the work of Frankel et al. (2018) and Wirth et al. (2018). These broadband ground motions are generated using a hybrid approach, where low frequency (<1 Hz) waveforms are simulated in a 3D seismic velocity model using SPECFEM3D and are combined with high frequency (1-10 Hz) waveforms modeled stochastically. We build these scenarios using a logic tree approach, varying the event magnitude, the down-dip and up-dip limits of slip, including rupture onto secondary splay faults, and the slip distributions, which are varied both randomly and based on interseismic geodetic locking. Ultimately, these ground motions may be coupled with simulations of tsunami inundation to achieve a time-dependent understanding of seismic and tsunami hazard in coastal communities. These simulations will also be used to quantify the impacts to infrastructure and cascading hazards, such as landslides, liquefaction, and land-level change, with a focus on coastal communities in the Pacific Northwest. In addition, we highlight a subset of earthquake scenarios to evaluate how different rupture properties, as well as methods for calculating static displacements (i.e., 3-D simulations vs. a 1-D Okada model), impact estimates of coastal vertical land-level change and their comparison to paleoseismic estimates from past earthquakes. We show that the method used to calculate vertical displacements influences the distribution of coseismic uplift and subsidence, and therefore has implications for comparisons to paleoseismic data from previous Cascadia earthquakes.

Additional Authors

Session: 3D Wavefield Simulations: From Seismic Imaging to Ground Motion Modelling - II

Type: Oral

Room: K’enakatnu 6

Date: 5/2/2024

Presentation Time: 11:30 AM Pacific

Presenting Author: Zheng Zhou

Description

The variability in spatial resolution of seismic velocity models obtained via tomographic methodologies is attributed to many factors, including inversion strategies, ray path coverage, and data integrity. Integration of such models, with distinct resolutions, is crucial during the refinement of community models, thereby enhancing the precision of ground motion simulations. Toward this goal, we introduce the Probability Graphical Model (PGM), combining velocity models with heterogeneous resolutions and non-uniform data point distributions. The PGM integrates data relations across varying-resolution subdomains, enhancing detail within low-resolution domains by utilizing information and a priori knowledge from high-resolution subdomains through a maximum likelihood problem. Assessment of efficacy, utilizing both 2D and 3D velocity models—consisting of synthetic checkerboard models and a fault zone model from Ridgecrest, CA—demonstrates noteworthy improvements in accuracy. Specifically, we find reductions of 30% and 44% in computed travel-time residuals for 2D and 3D models, respectively, as compared to conventional smoothing techniques. Unlike conventional methods, the PGM's adaptive weight selection facilitates preserving and learning details from complex, non-uniform high-resolution models and applies the enhancements to the low-resolution background domain.

Additional Authors

Session: Anisotropy Across Scales [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Chuntao Liang

Description

The Wave Gradiometry Method(WGM) has emerged as a powerful multipurpose tool to extract strain and rotation tensor, identify phases, and most importantly to image the earth structure. The WGM measures the spatial gradients of the wavefield within a subarray to extract 4 major attributes: phase velocity, wave directionality, geometrical spreading and radiation pattern. These attributes can be further used to extract 3D shear wave velocity and 3D azimuthal anisotropy. The WGM method is combined with the ambient noise Tomography (ANT) to the USARRAY in Alaska to obtain a 3D shear wave velocity structure and azimuthal anisotropic model. Our results reveal complex anisotropic patterns related to subduction structures. The fast directions in the Aleutian fore-arc region show a depth-dependant pattern associated with overriding lithospheric plate, fore-arc mantle wedge, subducting plate, and sub-slab mantle in the fore-arc region, respectively.We also notice that there are different fast directions in the Pacific Plate and the Yakutat Plate, implying different sources of anisotropy for each. An annular anisotropic pattern is present behind the arc at the northeastern edge of the subducting plate, which could be induced by the toroidal asthenospheric flow at the plate margin. Furthermore, our results provide a new evidence for the existence of the subducting plate beneath the Wrangell Volcanic Field.

References：

Cao F H, Liang C T. 2022, 3D velocity and anisotropy of the southeastern Tibetan plateau extracted by joint inversion of wave gradiometry, ambient noise, and receiver function, Tectonophysics, https://doi.org/10.1016/j.tecto.2022.229690

Liang, C., Liu, Z., Hua, Q., Wang, L., Jiang, N., & Wu, J. (2020). The 3D seismic azimuthal anisotropies and velocities in the eastern Tibetan Plateau extracted by an azimuth‐dependent dispersion curve inversion method. Tectonics, 39, e2019TC005747. https://doi.org/10.1029/2019TC005747

Langston, C. A. (2007). Wave gradiometry in two dimensions. Bulletin of the Seismological Society of America, 97(2), 401–416. https://doi.org/10.1785/0120060138

Additional Authors

Session: Induced Earthquakes: Source Characteristics, Mechanisms, Stress Field Modeling and Hazards [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Jenna L. Faith

Description

With increasing earthquakes in the Delaware Basin since 2009, earthquake studies, including accurate hypocenters, are critically needed in the Delaware Basin to identify the structures producing earthquakes, and to determine if they are related to unconventional petroleum development and production. In 2018, with funding from the Texas Seismological Network (TexNet), the University of Texas at El Paso deployed and maintained a network of 25 Magseis Fairfield Z-Land Generation 2 5-Hz seismic nodes in the Pecos, Texas region of the Delaware Basin, known as The Pecos Array. The network was deployed from November 2018 until the beginning of January 2020, with an additional two months of data recorded in September and October 2020. The network collected continuous 3-component data with a 1000-Hz sampling rate. The spacing of the nodes varied from ~2 km in town to ~10 km farther away from the city center. The Pecos Array was used to conduct a local 3-D P-wave tomography study in the Pecos, Texas region using the SIMULPS software. Previous tomography studies have been conducted to derive a P-wave velocity model of the entire Permian Basin, but these studies covered a broader area, and their best velocity results were in the upper 35 km of the crust. With our denser array, localized earthquakes, and increased ray coverage in the Pecos, Texas area, we have created a detailed 3-D velocity model for the top 8 km of this region. We observe velocity values that are consistent with reported geologies in the basin, and slower velocities on faults compared to areas without faults. We found that our new model is ~25% slower between depths 2 – 6 km compared to the DB1D regional velocity model that TexNet uses to locate their public catalog.

Additional Authors

Session: Six Decades of Tsunami Science: From the Source of the 1964 Tsunami to Modern Community Preparedness - I

Type: Oral

Room: Kahtnu 1

Date: 5/2/2024

Presentation Time: 03:00 PM Pacific

Presenting Author: Lisa Grant Ludwig

Description

As stated in the session description “educating the public, counteracting disaster amnesia and preserving the memories of tsunamis for future generations are all important tasks that the tsunami community will be working on for decades.” Perhaps the biggest challenge is motivating coastal communities and individual residents to ACT on the education, knowledge and memories to prepare for future tsunamis. Social scientists developed the Protective Action Decision Model to describe how individuals are motivated to take action to protect themselves from natural and other hazards. Public health researchers have developed and tested health behavior theories for application in campaigns to improve public health. These theories include the health belief model, ecological model and self-efficacy model. According to the health belief model, there are several factors that motivate a change in behavior when a person is faced with a threat. These factors include the extent to which a person feels vulnerable, the perceived danger or severity of the threat, the real or perceived barriers to taking action, and the perceived effectiveness of taking action. The self-efficacy model includes a sense of control, which overlaps with factors in the health belief model. The ecological model of behavior focuses on the social environment, including individual “intrapersonal”, interpersonal, institutional and community factors, as well as public policy. A health promotion program would incorporate elements of these 3 models to motivate behavioral change. A typical health promotion campaign would have the following elements that are directly relevant to tsunami risk reduction: 1) Belief in personal threat, e.g. “I am susceptible to tsunami”; 2) Belief in response efficacy, e.g. “There is something I can do that will lessen tsunami threat”; 3) Belief in personal efficacy, e.g. “ I am capable of taking action”; and 4) Belief that new behaviors are consistent with group norms, e.g. “My peers support this action”.

Additional Authors

Session: Seismoacoustic, Geodetic and Other Geophysical Investigations of Active Volcanoes - I

Type: Oral

Room: Kahtnu 2

Date: 5/3/2024

Presentation Time: 08:45 AM Pacific

Presenting Author: Maochuan Zhang

Description

Axial Seamount is a submarine volcano at the intersection of the Cobb hotspot and the Juan de Fuca Ridge. The last eruption in 2015 was recorded by 7 ocean bottom seismometers on the Ocean Observatories Initiative Regional Cabled Array. A small number of manual composite focal mechanisms (FMs) obtained by Levy et al. (2018) confirmed that the motion on an outward dipping ring fault beneath the summit caldera reversed during the 2015 eruption. Our earthquake catalog for Axial Seamount comprises ~150,000 hypocenters from 2015-2024. A large data set of FMs would provide constraints on the geometry and deformation of the caldera ring faults, the impacts of magma movement and hydrothermal process on faulting, and the evolution of crustal stresses through the eruptive cycle. To generate FMs automatically, we incorporate the methodology of Shelly et al. (2016) which determines polarities by maximizing congruence with signed waveform correlation coefficients. We first tested the approach on subsets of 5000 earthquakes from the east and west walls of the caldera. We obtained 53,000 polarities which show a 95% consistency with the sign of the cross-correlation coefficients and a 99% accuracy rate when benchmarked against 3,000 manual picks. Considering just earthquakes with at least five polarities and 5 S/P amplitude ratios, we created 680 groups of ~15 earthquakes with fully consistent polarities and similar locations and S/P ratios. Finally, we used the HASH program to generate composite FMs. The hypocenters beneath the west wall mostly fall on an outward dipping ring fault and most FMs are normal faults consistent with this fault plane. The hypocenters in the test data set beneath the east wall have a more complex distribution and the focal mechanism similarly show more variation, consistent with the influence of ring faulting and deformation in the regions where dikes are injected during spreading events. We are presently extending the approach to the entire catalog and based on the number of earthquakes with sufficient polarities and S/P ratios, expect to obtain ~7,000 composite FMs.

Additional Authors

Session: Structure and Behavior of the Alaska-Aleutian Subduction Zone - II

Type: Oral

Room: Tikahtnu Ballroom A

Date: 5/3/2024

Presentation Time: 10:45 AM Pacific

Presenting Author: Valeria Cortés Rivas

Description

What determines megathrust slip behavior in subduction zones is still under debate, and the relationship between the preferred slip style over short, earthquake-cycle time scales and long-term patterns of deformation also remains poorly understood. We collected multichannel seismic data, USGS legacy reflection data, and gravity data in the Andreanof segment of the Aleutian Islands to address these questions. This region presents contrasting seismic and locking behavior from west to east. There is a higher recurrence of large earthquakes and tsunamis and higher coupling in the western section. Moreover, the oblique subduction leads to strain partitioning. As a consequence, the upper plate developed strike-slip faults and rotating blocks, impacting the distribution of compressional and extensional stress.

Observations indicate distinct forearc deformation styles in the eastern region (Atka) and the western region (Adak). Atka has a wide forearc basin with flat layers, whereas Adak shows more compression by uplifting the frontal prism and forearc basin shortening, which correlates with the higher recurrence of megathrust earthquakes. Adak shows intracrustal reflectors that could be magmatic intrusions, underplating, or old deformational features.

The incoming plate properties, sediments, and trench infill show similar characteristics in the entire Andreanof segment. Thus we propose that over-riding plate properties contribute to the different seismic and deformational styles. The combination of differences in rheology due to magmatic intrusions, underplating, and/or pre-existing deformation and differences in tectonic stress associated with rotating blocks and the strike-slip systems could impact fault development and changes in forearc permeability. We explore the hypothesis that the higher shortening in the western section could be more efficient in releasing pore fluid pressure, increasing the effective stress, which promotes coupling and deformation.

Additional Authors

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Su Young Kang

Description

Nakdong River is one of the major rivers in Korea that runs through the Busan metropolitan area. During the 1.6 km long bridge construction across the river, twenty-seven boreholes were drilled to measure the depth of the bedrock. This study determines the resonance frequencies at the borehole sites using the HVSR (Horizontal-to-vertical spectral ratio) technique and compares the results with direct measurements. Bedrock depths from the 27 borehole measurements vary from 38 to 70 meters. Although their variations are not serious along the 3.8 km long route, a relatively sharp decrease in the bedrock depth was noticed near the borehole NSB-5 (~38 meters). We collected ambient noise data at locations near 27 boreholes in 2022 and estimated resonant frequencies using the HVSR technique. Resonance frequencies from HVSR vary from 0.9 Hz to 1.3 Hz. A relatively high resonance frequency, 1.3 Hz, is estimated at NSB-5, which is consistent with the observations from the direct measurements from boreholes. Details of the boring logs indicate that the sedimentary layers consist of multiple lithologic layers, including reclaimed soil, silt sand, silt clay, and sand-mixed silt gravel. Since their impedance contrasts are not significant, it is not evident from the HVSR curves. This study demonstrated a significant correlation between the depth of bedrock identified in boreholes and the resonance frequency obtained through HVSR analysis using microtremor observations. HVSR analysis effectively reflected the bedrock depth at the microtremor observation sites.

Additional Authors

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Katleen Wils

Description

Lacustrine paleoseismology has evolved into a primary technique to reconstruct the recurrence of ground motion at a given site. Different types of sedimentary shaking imprints (e.g., turbidites, landslides) have been linked to various seismic ground motion parameters (e.g., intensity, duration, frequency content). Understanding the depositional characteristics of such imprints thus has great potential to improve local seismic hazard estimations. By defining ground-motion threshold values for the appearance and absence of certain coseismic imprints, earthquake magnitude and source location can be estimated via ground-motion modelling. However, up to now the input for these models has remained limited to rather qualitative measures of strong ground motion that are poorly physically constrained (i.e., macroseismic intensity). This is partly related to the gap in our understanding of the site characteristics of lake sediments, as direct observations of seismic shaking on the bottom of a lake are scarce.

To get a first idea on the variability of ground-shaking site effects in lakes and how these relate to the depositional environment, we study two sites in southern Chile and south-central Alaska located at ~200 km from the subduction trench by analyzing ambient noise geophone array registrations as well as hammer seismic data. The Alaskan site consists of a 4.4 km² drained proglacial lake in mountainous terrane (Iceberg Lake) containing ~1500 years of outcropping sediments in an actively eroding environment. In Chile, measurements were performed along the shores of the 860 km² piedmont Lago Llanquihue, where lake sediments with an (up to now) unclear age are buried at shallow depth. Preliminary analysis shows that Vs30 values are very similar, while H/V spectral ratios and fundamental frequencies are more variable within and between sites, emphasizing the need for detailed site studies in any lacustrine paleoseismic study. Ongoing analysis will focus on understanding the origin of these differences, and how this knowledge can contribute to the interpretation of other lacustrine paleoseismic records.

Additional Authors

Session: Seismic Monitoring, Modelling and Management Needed for Geothermal Energy and Geologic Carbon Storage [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/2/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Braden A. Hoefer

Description

Midcontinent seismic activity in the United States has sharply increased from background levels in the last 15 years. Oklahoma has been at the center stage for this increase due to the production of oil and gas and the associated injection of fracking fluids and wastewater disposal. While there were notable large earthquakes, such as the M5 Cushing and Pawnee events, there are a vast number of smaller events; detecting and cataloging these events can provide valuable insight into the evolution of the subsurface, leading to better industry practices and a more robust understanding of the impact that fluid injection has on fault activations. Here, two methods are employed to detect small earthquakes using continuous waveform with a dense nodal array near Cushing, Oklahoma. Array-beamforming detection requires no prior knowledge of the region's waveform or local velocity model, which detects events by comparing inter-station waveform similarity. LOC-FLOW is a machine learning-based workflow combining several algorithms to detect and locate earthquakes. Both methods have been shown to detect more events than are contained in previous catalogs and, if automated, can be a hands-off approach to creating catalogs of high resolution. The merits and drawbacks of each method must be understood to apply them most appropriately. The array-beamforming method detected thousands of events compared to the machine learning method's 112 events for the same period. However, array-beamforming is susceptible to detecting non-tectonic events such as passing traffic, perhaps owing to its roadside deployment. Event location remains variable between earthquakes detected by both methods, with an average offset of 3.18 km between the 43 co-detected events. Fine-tuning processing parameters will improve the beamforming event detection to remove false detections, such as increasing the maximum inter-station distance for which waveform similarities are compared, increasing the duration of the time window over which waveforms are compared, or considering different sub-arrays. Further characterization of detected events will be performed.

Additional Authors

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned - III

Type: Oral

Room: Tubughnenq’ 5

Date: 5/2/2024

Presentation Time: 08:30 AM Pacific

Presenting Author: Colin N. Pennington

Description

The association of phase picks to form events is one of the most fundamental components of seismology. Any error in association due to the inclusion of errant phase picks will introduce errors in the later characterization of the event, such as its location, magnitude, and focal mechanism. Large and dense sensor networks, such as nodal arrays (and DAS), offer unique challenges in association due to vast number of observations, high likelihood of errant picks or multiple events occurring within the array at the same time. Also the large number of stations can greatly increase the time it takes to perform the association. For this reason, machine learning might provide a more optimal method of association. In this work, we examine how well machine learning methods (e.g., GaMMA, Phaselink, and GENIE) can incorporate dense nodal arrays into regional networks and how well they handle the density of stations. We test their capabilities on two nodal deployments, one within Rock Valley Nevada (80 Nodes), and the LArge-n Seismic Survey in Oklahoma (LASSO) dense nodal array (>1800 nodes). These two nodal arrays will test two particular issues that the machine learning algorithms might face: 1) The Rock Valley Array is a small array (<10 kms) within a large regional network and it will allow tests of how the algorithms are able to merge the two during association. 2) The Oklahoma LASSO array spans 10’s of kms and contains multiple earthquake sequences and it will allow tests of each algorithm’s ability to associate events that might be happening simultaneously. We then compare their associated bulletins to those obtained using Rapid Earthquake Association and Location algorithm (REAL), a more traditional method of association. We find that there are often vast differences between findings of certain methods. Some methods finding roughly half the events of others while others cannot integrate the nodal array with the regional network. We even find that certain methods break apart larger events into multiple events. Prepared by LLNL under Contract DE-AC52-07NA27344.

Additional Authors

Session: Understanding and Quantifying the Variability in Earthquake Source Parameter Measurements [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Giovanna Calderoni

Description

Seismic spectral estimates of earthquake stress drop remain controversial, subject to large uncertainties, despite the fundamental role the source parameter plays in assessing the seismic forecasting in a given area and in improving ground motion predictions for seismic hazard mitigation. Comparing different measurement techniques to understand how analysis processes affect the resulting estimates of stress drops is a necessary first step to improve resolution. It can also be useful to perform the same procedures using different data sets. In this study we focus on the Pollino area, southern Apennines, where structural complexities are thought to control seismic activity. We compare estimates of the Brune-style stress drop for 100 earthquakes (M2.2-5.2) derived from two techniques: spectral fitting for attenuation, site effects and source), and spectral ratio fitting in which an empirical Green’s function event is assumed to remove the path and site effects. In all cases, the Brune (1970) source is assumed. In the spectral fitting we first assume a regional attenuation model, and second estimate path attenuation from the high-frequency decay of 8 well-recorded earthquakes (M3.6-5.2), to obtain attenuation-corrected spectra. We estimate and remove the site term in both cases by averaging the attenuation-corrected spectra for each event, and then computing the difference from the mean event spectrum for each station (assuming the mean site correction is zero). These differences are averaged over the event ensemble to obtain a mean site term for each station, which is then removed before fitting the resulting estimates of source spectra to obtain the final source parameter estimates. In the EGF approach, we divide the spectra of the target events by those of co-located smaller EGF earthquakes, and fit the resulting spectral ratios, for each event, at each station, assuming all path and site effects are removed. We perform the fitting first with no constraints on the stress drop (and corner frequency) of the EGF event, and then with constraints based on different scaling laws of stress drop to seismic moment.

Additional Authors

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned - III

Type: Oral

Room: Tubughnenq’ 5

Date: 5/2/2024

Presentation Time: 08:45 AM Pacific

Presenting Author: Avigyan Chatterjee

Description

The state of Nevada is one of the most seismically active areas of the United States, with numerous active fault systems throughout the Walker Lane and Basin and Range tectonic faults. Despite high rates of seismic activity, Nevada currently lacks a comprehensive catalog of earthquake focal mechanisms that could be used to better understand seismotectonic processes. Determining the focal mechanisms of small earthquakes poses a considerable challenge due to the difficulty of distinguishing phase arrivals and first-motion polarities from noise. To address this issue, we augment the first-motion polarity database maintained by the Nevada Seismological Laboratory with additional measurements obtained using a convolutional neural network algorithm. We then complement polarity data with new measurements of S/P amplitude ratios to provide additional constraints on event mechanisms. By incorporating both existing and newly obtained data, we construct a comprehensive focal mechanism catalog for the state of Nevada from 2008 through 2023, utilizing a revised implementation of the HASH method originally developed by Hardebeck and Shearer (2002). With the new focal mechanism catalog, we analyze changes in focal mechanism characteristics resulting from significant mainshocks like the 2020 Mw6.5 Monte-Cristo and other prominent earthquake sequences like the Spanish Springs, Hawthorne, Nine-Mile Ranch, and Sheldon sequences. The enhanced resolution of the new catalog will play a crucial role in advancing our understanding of the crustal stress field, mechanisms triggering earthquakes, fault zone geometry, and strain partitioning across the state.

Additional Authors

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Raul Benjamin Mendoza

Description

The southern Coast Mountains of British Columbia are situated in the inner northern forearc of the Cascadia Subduction Zone. They are traditionally viewed as the static backstop for the northward moving Oregon coast block. While many faults have been mapped in the Coast Mountains, conclusive evidence of Holocene displacement has not been observed. The recent discoveries of surface ruptures along the Leech River, Beaufort Range, and XEOLXELEK-Elk Lake faults on neighboring Vancouver Island underscore the importance of reexamining the faults in the southern Coast Mountains, which could pose a significant hazard to densely populated areas including Metro Vancouver. However, this effort is challenged by glaciated, mountainous geomorphology, and dense vegetation.

We collated digital elevation models of varying coverages and scales, from 1-arc-second satellite data to meter-scale lidar data. Particular attention was paid to locations of previously mapped faults and seismicity. We identified escarpments related to regional-scale lineaments at Bowen Island, Alouette Lake, Coquitlam Mountain, and Nahatlatch Lake, in addition to known fault systems such as the Fraser River Fault. We conducted field surveys in 2022 and 2023 to collect ground observations where the linear features appear to intersect Holocene sediments. In some areas, we deployed a UAV lidar scanner to obtain ultra-high resolution topographic data. At one site in the Britannia Shear Zone, we observed a 20-cm offset in the soil profile on opposite sides of a fault exposure, but the UAV lidar did not reveal a scarp extending from the outcrop. In addition to vegetation cover and glacial erosion, we have been challenged by unpredictable weather, difficult access to remote sites, and a lack of sufficiently fine-grained Holocene sedimentary deposits to potentially record sub-meter-scale displacements. Future plans include helicopter-based lidar surveys of remote areas and sub-bottom profiling in lakes that may better preserve offsets in Holocene stratigraphy. The results of this project will be incorporated into Canada’s national seismic hazard and risk models.

Additional Authors

Session: Seismic Monitoring, Modelling and Management Needed for Geothermal Energy and Geologic Carbon Storage [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/2/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Yingcai Zheng

Description

As geological carbon storage (GCS) is being adopted worldwide, monitoring possible CO2 migration in the subsurface is needed to ensure conformance and containment. A scalable turnkey solution is favored over repeated dense data acquisition (4D seismic) for GCS monitoring. Expensive time-lapse 3D seismic monitoring has been used in CO2-enhanced oil recovery (EOR) fields, but its use in GCS is not economically feasible. We propose a cost-effective GCS monitoring approach using localized seismic waves and permanent source arrays. Given the spatially finite nature of the localized wave, we only need a few geophones on the surface to record scattered localized seismic wavefields. To quantify the amount of CO2 using time-lapse changes of localized seismic waves, we conduct lab measurements of the P-wave velocity and density for supercritical CO2-saturated brine under various pressure-temperature conditions and a fluid substitution equation. Our monitoring approach using localized seismic waves could be a turnkey solution to cost-effective, long-term GCS monitoring.

Additional Authors

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - IV

Type: Oral

Room: K’enakatnu 6

Date: 5/1/2024

Presentation Time: 05:00 PM Pacific

Presenting Author: Jhardel Dasent

Description

A hallmark of many processes in Earth's subsurface [e.g., landslides, ground-rupturing earthquakes, liquefaction, and crystal-rich magmas] is the transitions in states that granular assemblages undergo, from structurally arrested to creeping to flowing. The frictional jamming and material memory theoretical frameworks argue that volume fraction and shear stress govern such transitions and that the material records the transitions. We use x-ray microtomography to determine if the three-dimensional re-arrangement and fracturing of grains within assemblages collected from two paleoseismic sites along the southern San Andreas fault record frictional jamming phenomenologies. Analyses reveal that fault zone granular assemblages transition between one or more interrelated but geometrically localized and mesoscopic deformation states that change assemblages' stability during the seismic cycle. These states include [1-2] bulk and localized grain re-arrangements, [3] individual grain fracturing, and [4] localized zones of grain fracturing. Grain re-arrangement is primarily a global phenomenon. Grain size and non-rattlers exert control over grain fracturing and re-arrangements. Coseismic shear erases anisotropic fabric memory developed during aseismic shear and introduces its own. Shear stress magnitude and elastoplasticity control memory creation and erasure and thus vary with distance from a fault strand. Our findings imply [1] that sheared fault zone sediments experience a cycle of memory creation and erasure accompanied by differing deformation phases and thus hold an invaluable record of how shallow faults move coseismically and aseismically, and [2] that frictional jamming and material memory remain promising unifying theories for granular flow, even considering naturally imposed disorder.

Additional Authors

Session: From Earthquake Recordings to Empirical Ground-Motion Modelling - II

Type: Oral

Room: Tubughnenq’ 4

Date: 5/2/2024

Presentation Time: 10:45 AM Pacific

Presenting Author: Feiruo Xia

Description

The proliferation of seismic record repositories through the expansion of seismic networks and high-performance computer simulations of earthquake scenarios, have made available ground-motion databases rich enough to make possible data-driven models of ground-motion synthesis that account for complex site effects. Data-driven methods offer a novel approach to describing these processes by directly learning the governing laws from sufficiently rich training data, while avoiding the use of simplified assumptions that limit the realism of models developed with traditional statistical tools. In this study, we demonstrate this new paradigm of learning the underlying physics in a data-driven framework –and quantifying as such, the sources of ground motion epistemic uncertainty, by coupling: (i) a Generative Adversarial Neural Operator (GANO), which synthesizes broadband three-component acceleration time histories at reference outcrop conditions, with (ii) a Fourier Neural Operator (FNO), which modifies the outcrop ground motions to account for the full nonlinear response of the near-surface soil layers. GANO was trained on a synthetic ground motion dataset for strike-slip and reverse events developed using the Southern California Earthquake Center (SCEC) Broadband Platform (BBP), while FNO was trained on non-linear one-dimensional wave propagation through smooth Bay Area velocity profiles using the site-response software, PySeismoSoil. A key advantage of the neural operator architectures in GANO and FNO compared to traditional neural networks, is their ability to learn the mapping between continuous function spaces as opposed to finite-dimensional sets, rendering the training and application of the model resolutions invariant (i.e., training can include input signals of different sampling frequencies without loss of information or generation of artifacts, while prediction can be performed on sampling frequencies independent of training). Verification analyses through residual and goodness of fit evaluations demonstrate that GANO can learn the magnitude and distance scaling, while FNO can correctly estimate the non-linear amplification for ground motions and profiles not included in the training dataset for 0.1 to 30hz frequency range. By appropriately conditioning data-driven algorithms, or combinations thereof like in this case, our work demonstrates the potential of using these methods to learn increasingly complex physics and their uncertainty over the entire frequency range of engineering interest, and to generate on demand time-histories appropriate for engineering design with high degree of realism. 

Additional Authors

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Ethan F. Williams

Description

Completed in February 2012, the Seattle Liquefaction Array (UW.SLA) has now recorded more than a decade of continuous borehole acceleration and pore pressure data at a liquefaction-susceptible site in Seattle’s south of downtown (SODO) neighborhood. While the seismically quiescent Pacific Northwest has not produced any earthquakes with appreciable excess pore pressure generation at SLA during the past decade, the urban ambient seismic noise of industrial south Seattle provides a rich dataset for near-surface investigations. Quasi-static surface loading from trains passing by or parking only 5-30 m from SLA drives pore pressure transients as large as 1 kPa at 52 m depth. By computing downhole horizontal-component cross-correlations with overlapping 40-s windows, we can measure perturbations in near-surface velocity from ballistic shear waves ~1-50 Hz generated by the trains. Combining these two datasets, we estimate the nonlinear elastic response of the sediment to poroelastic stress changes, which is as large as +20% dv/v (averaged 0-60 m) per 300 Pa (measured at 52 m). We also apply ambient noise coda wave interferometry to study changes in near-surface velocity and attenuation over seasonal to decadal scales. In the coda of vertical component cross-correlations, we find a decade-long monotonic stiffening trend, with 1-10 Hz Rayleigh wave phase velocity increasing by ~4% from 2012 to 2022. The horizontal-component and cross-component correlations are more complex, showing opposing seasonal trends in dt/t at different windows in the coda and different frequencies, likely representing a depth-dependent phase lag in poroelastic and/or thermoelastic velocity changes.

Additional Authors

Session: Numerical Modeling in Seismology: Developments and Applications - II

Type: Oral

Room: Tubughnenq’ 4

Date: 5/1/2024

Presentation Time: 10:45 AM Pacific

Presenting Author: Paul Cupillard

Description

Non-periodic homogenization has proved to be an accurate asymptotic method for computing long-wavelength equivalent media for the seismic wave equation, turning small-scale heterogeneities and geometric complexity into smooth elastic properties. Using homogenized media allows i) decreasing the computation cost of wave propagation simulation and ii) studying the apparent, small-scale-induced anisotropy. After illustrating these two aspects briefly, we propose to analyze in great detail the accuracy of body waves simulated in homogenized 3D models of the subsurface. First, the behaviour of head-, reflected and refracted waves with respect to source-receiver offset, maximum frequency and velocity contrast across a planar interface, is investigated. Then, we consider the SEG-EAGE overthrust model to exemplify how the accuracy of simulated body waves anti-correlates with the distance to seismic source and the amount of apparent anisotropy. In high apparent anisotropy regions, we show that the first-order correction provided by the homogenization theory significantly improves the computed wavefield. The overall results of this analysis better frame the use of homogenized media in seismic wave simulation.

Additional Authors

Session: 3D Wavefield Simulations: From Seismic Imaging to Ground Motion Modelling [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/2/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Yuan Tian

Description

Sedimentary basins trap seismic waves, leading to amplification and long-duration shaking. This seismic response of a sedimentary basin can be relevant both for understanding active tectonics and for assessing seismic hazards relevant to society. Using 3D seismic wavefield simulations with different models, we can explore how the basin depth and the basin’s geometrical boundary affect the seismic waves, amplitudes, and radiation patterns. Nenana basin in central Alaska is a promising region for studying basin wave propagation because its basement surface has been estimated from detailed active-source imaging and because there were about 15 broadband seismic stations in the region, enabling comparisons between simulation results (synthetics) and observations (data). We have created four Nenana basin region models: 1) the Berg et al. (2020) 3D tomographic model, 2) the Berg model with an embedded basin model, 3) a simplified model of an elliptical basin embedded in the Berg model, 4) a model with upper 8km from 1D velocity profile from Brocher2008 and bottom from the Berg model. By comparing and analyzing the seismic simulation results in both time and frequency domains from these models, together with the real data collected in this region, we can investigate the detailed mechanism of basin amplification for a variety of different seismic sources, basin geometries, and frequencies.

Acknowledgments

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This manuscript was reviewed and released LLNL-ABS-859040

Additional Authors

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Nealey E. Sims

Description

We use network-matched filtering (NMF) and relative earthquake relocation techniques to derive a detailed catalog of earthquake locations for the Minto Flats fault zone (MFFZ) in interior Alaska between September 2014 and December 2019. The MFFZ is a left-lateral strike-slip fault system situated between the right-lateral Denali and Kaltag faults. It produced a magnitude-6 earthquake in 1995 and has potential for a magnitude-7 earthquake. We systematically test parameters for the NMF and earthquake relocation routines and perform a qualitative check on the final catalog in order to reduce false detections that would skew relocations. Our results provide the most complete catalog for the MFFZ and include deeper events, clusters of shallow seismicity and a complex, and segmented fault structure not observed in the original regional catalog. We are also able to determine the fault orientation of the northwest cluster of seismicity containing the 2014 Mw 5.0 event as well as identify a previously unstudied third strand segment in the southwest region of the fault zone.

Additional Authors

Session: The 2023 USGS National Seismic Hazard Model and Beyond [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM Pacific

Presenting Author: Yuehua Zeng

Description

I apply a fault-based crustal deformation model with buried dislocation sources to estimate on-fault slip rates and off-fault moment rate distribution in Alaska for the long-term National Seismic Hazard Model (NSHM). This model uses the method of Zeng and Shen (2017) to invert for slip-rate and strain-rate parameters based on inputs from Global Positioning System (GPS) velocities and geologic slip-rate constraints. A time-dependent postseismic deformation correction is applied to the data to account for the viscoelastic responses from the 1964 Great Alaska earthquake. I modify the Alaska subduction model from the block model of Elliott and Freymueller (2020) using the USGS Slab2.0 model (Hayes et al., 2018). Faults in Alaska are obtained from the 2023 NSHM Alaska geologic fault model (Powers et al., 2023). The model slip rates are determined using a least-squares inversion. The resulting on-fault model slip rates are compared with the geologic slip rates in Alaska, and the off-fault moment rate is compared with the regional seismicity rate.

Additional Authors