Relationship between peak and cumulative ground motions from 49 Mw 3-6 earthquakes in the San Francisco Bay Area

Bulletin of the Seismological Society of America
By: , and 

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Abstract

We examine the relationship between peak ground velocity (PGV) and cumulative absolute displacement (CAD) for 49 Mw 3 – 6 earthquakes in the San Francisco Bay Area (SFBA) and gain insight into the spatiotemporal partitioning of seismic energy in ground motion records with respect to source, path, and site effects. PGV and CAD are positively correlated, but there can be large deviations from the average trend. For example, ground motion records with either very long duration resonance or short pulse-like motions will have higher or lower CAD, respectively, but could have very similar PGV. We perform principal component analysis (PCA) on PGV-CAD for >7000 records in the SFBA with the goal of investigating what influences positive or negative anomalies in cumulative motions. PCA rotates the PGV-CAD datapoints into two principal components, where the one with the larger variance, which we call the “primary intensity” represents mostly the distance-dependence of ground motion amplitudes. The other principal component, which we call the “excess motion”, represents the deviation from cumulative motions that would be typical for a ground motion record with a given PGV. The excess motion will be positive in the case of records with long duration ringing and will be negative for short duration pulse-like ground motions. We find that excess motion is generally positive at sites in sedimentary basins and in soft sediments around the SF Bay. Excess motion is generally negative in the very near field, as well as at sites on hard bedrock. We discuss the findings here in terms of implications for seismic hazard applications and other wave propagation phenomena.

Suggested Citation

Hirakawa, E.T., Parker, G.A., and Baltay, A.S., 2025, Relationship between peak and cumulative ground motions from 49 Mw 3-6 earthquakes in the San Francisco Bay Area: Bulletin of the Seismological Society of America, v. 115, no. 5, p. 2355-2370, https://doi.org/10.1785/0120240257.

ISSN: 1943-3573 (online)

Study Area

Publication type Article
Publication Subtype Journal Article
Title Relationship between peak and cumulative ground motions from 49 Mw 3-6 earthquakes in the San Francisco Bay Area
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120240257
Volume 115
Issue 5
Publication Date June 24, 2025
Year Published 2025
Language English
Publisher Seismological Society of America
Contributing office(s) Earthquake Science Center
Description 16 p.
First page 2355
Last page 2370
Country United States
State California
City San Francisco
Other Geospatial San Francisco Bay area
Additional publication details