Earthquake Ground Motion Insights From the USGS Lake Almanor, California, Aftershock Nodal Array Deployment
Description:
We investigate both source effects, such as rupture directivity, and the effects of shallow geologic structure on site response, in a ground-motion analysis of aftershocks of the May 11, 2023, M5.5 and May 12, 2023, M5.2 Lake Almanor, California, earthquakes. The Lake Almanor earthquakes occurred near the 2013 M5.7 Canyondam earthquake sequence in the vicinity of Canyon Dam, an embankment dam on the north fork of the Feather River used for hydroelectricity generation. The 2023 M5.5 and M5.2 earthquakes both caused MMI 6 shaking and generated over 7000 and 1000 felt reports, respectively. On May 12, the U.S. Geological Survey deployed 34 nodal seismometers (nodes) around Lake Almanor in an approximately 40 by 25 km array that recorded more than 25 M > 2.5 aftershocks over the following 2 months at epicentral distances as small as 5 km and with dense azimuthal coverage. The nodes recorded continuous 3-component waveforms at a 2-ms sampling interval, and have been validated against permanent network seismic instrumentation. We use the USGS software gmprocess (Hearn et al., 2019) to perform quality control, apply filters and baseline corrections, and to compute waveform intensity measures (IMs) from the recorded nodal data and data from regional seismic networks. We compute residuals between a ground-motion model and the observed IMs, and then partition them into components representing repeatable source, path, and site effects. We utilize the azimuth distribution of stations to investigate rupture directivity effects and the correlation of path and site effects with the regional geologic structure. We leverage information about path and site effects from the recorded aftershocks to improve our understanding of the M5.5 and M5.2 earthquakes. Results from this analysis could be used to improve seismic hazard characterization for infrastructure in the Lake Almanor region.
Session: From Earthquake Recordings to Empirical Ground-Motion Modelling - II
Type: Oral
Date: 5/2/2024
Presentation Time: 11:30 AM (local time)
Presenting Author: Grace
Student Presenter: No
Invited Presentation:
Authors
Grace Parker Presenting Author Corresponding Author gparker@usgs.gov U.S. Geological Survey |
Annemarie Baltay abaltay@usgs.gov U.S. Geological Survey |
Evan Hirakawa ehirakawa@usgs.gov U.S. Geological Survey |
Rufus Catchings catching@usgs.gov U.S. Geological Survey |
Mark Goldman goldman@usgs.gov U.S. Geological Survey |
Joanne Chan jchan@usgs.gov U.S. Geological Survey |
Robert Sickler rsickler@usgs.gov U.S. Geological Survey |
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Earthquake Ground Motion Insights From the USGS Lake Almanor, California, Aftershock Nodal Array Deployment
Session
From Earthquake Recordings to Empirical Ground-Motion Modelling