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V_(S30) and Dominant Site Frequency (⁠f_d⁠) as Provisional Station M_L Corrections (⁠dM_L⁠) in California

Yong, Alan and Cochran, Elizabeth and Andrews, Jennifer and Hudson, Kenneth and Martin, Antony and Yu, Ellen and Herrick, Julie and Dozal, Jessica (2020) V_(S30) and Dominant Site Frequency (⁠f_d⁠) as Provisional Station M_L Corrections (⁠dM_L⁠) in California. Bulletin of the Seismological Society of America . ISSN 0037-1106. (In Press) https://resolver.caltech.edu/CaltechAUTHORS:20201006-151700069

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Abstract

New seismic stations added to a regional seismic network cannot be used to calculate local magnitude (⁠M_L⁠) until a revised regionwide amplitude decay function is developed. Each station must record a minimum number of local and regional earthquakes that meet specific amplitude requirements prior to recalibration of the amplitude decay function. Station component adjustments (⁠dM_L⁠; Uhrhammer et al., 2011) are then calculated after inverting for a new regional amplitude decay function, constrained by the sum of dM_L for long‐running stations. Therefore, there can be significant delay between when a new station starts contributing real‐time waveform packets and when data can be included in magnitude determinations. We propose the use of known estimates of seismic site conditions such as the time‐averaged shear‐wave velocity (⁠V_S⁠) of the upper 30 m (⁠V_(S30)⁠) and the site dominant frequency (⁠f_d⁠) to calculate dM_L⁠. Previously established dM_L⁠, measured V_(S30)⁠, and f_d data are available for between 126 and 458 horizontal components (east–west and north–south) at 81 seismic stations in the California Integrated Seismic Network; dM_L data range from −1.10 to 0.39, V_(S30) values range from 202 to 1464  m/s⁠, and 440 f_d values are compiled from earthquake and microseismic records that range from 0.13 to 21 Hz. We find V_(S30) and dM_L exhibit a positive coefficient of determination (⁠R=0.59⁠), indicating that as V_(S30) increases, dM_L increases. This implies that greater site amplification (lower V_(S30)⁠) results in smaller dM_L⁠. f_d and dM_L also generally exhibit a positive correlation (⁠R²<0.56⁠), which implies lower dM_L values are related to site resonance at depth‐dependent frequencies. Using the developed relationships, V_(S30) or f_d measurements can be used to establish a provisional dM_L for newly established stations. This procedure allows new stations to contribute to regional network M_L determinations immediately without the need to wait until a minimum set of earthquake data has been recorded.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1785/0120200130DOIArticle
ORCID:
AuthorORCID
Cochran, Elizabeth0000-0003-2485-4484
Andrews, Jennifer0000-0002-5679-5565
Additional Information:© 2020 Seismological Society of America. Manuscript received 24 March 2020; Published online 6 October 2020. The authors thank U.S. Geological Survey (USGS) Retirees Allan Walters and Robert Dollar for early discussions (2015). Recent remarks by Art Frankel and Eric Thompson were also helpful, specifically with our preliminary presentation at the 2018 Fall Meeting of the American Geophysical Union. Thomas Pratt and Zhigang Peng provided much encouragement for this publication. The authors are also grateful for feedback from Annemarie Baltay‐Sundstrom and USGS reviewers Clara Yoon and Glenn Biasi. Final USGS reviews by Shane Detweiler and Michael Diggles improved this article. Comments from journal reviewers Robert Uhrhammer and Dino Bindi were also deeply appreciated. Map in Figure 1 was generated using GMT software (Wessel et al., 2019). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Data and Resources: V_(S30) or f_d data in this study are provided as supplemental material.
Group:Seismological Laboratory
Record Number:CaltechAUTHORS:20201006-151700069
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201006-151700069
Official Citation:Alan Yong, Elizabeth Cochran, Jennifer Andrews, Kenneth Hudson, Antony Martin, Ellen Yu, Julie Herrick, Jessica Dozal; V_(S30) and Dominant Site Frequency (⁠f_d⁠) as Provisional Station M_L Corrections (⁠dM_L⁠) in California. Bulletin of the Seismological Society of America doi: https://doi.org/10.1785/0120200130
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105846
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:07 Oct 2020 00:09
Last Modified:07 Oct 2020 00:09

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