Premium
Semiautomated Estimates of Directivity and Related Source Properties of Small to Moderate Southern California Earthquakes Using Second Seismic Moments
Author(s) -
Meng Haoran,
McGuire Jeffrey J.,
BenZion Yehuda
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2019jb018566
Subject(s) - seismology , directivity , geology , seismic moment , centroid , deconvolution , focal mechanism , moment (physics) , moment magnitude scale , geodesy , magnitude (astronomy) , epicenter , range (aeronautics) , fault (geology) , geometry , statistics , mathematics , physics , scaling , telecommunications , materials science , classical mechanics , astronomy , computer science , antenna (radio) , composite material
We develop a semiautomated method for estimating with second seismic moments the directivity, rupture area, duration, and centroid velocity of earthquakes. The method is applied to 41 southern California earthquakes with magnitude in the range 3.5–5.2 and provides stable results for 28 events. Apparent source time functions (ASTFs) of P and S phases are derived using deconvolution with three stacked empirical Green's functions (seGf). The use of seGf suppresses nongeneric source effects, improves the focal mechanism correspondence to the analyzed earthquakes, and typically allows inclusion of 5 to 15 more ASTFs compared with analysis using a single eGf. Most analyzed earthquakes in the Trifurcation area of the San Jacinto Fault have directivities toward the northwest, while events around Cajon Pass and San Gabriel Mountain tend to propagate toward the southeast. These results are generally consistent with predictions for dynamic rupture on bimaterial interfaces associated with the imaged velocity contrasts in the area. The second moment inversions also provide constraints on the upper and lower bounds of rupture areas in our data set. Stress drops and uncertainties are estimated for elliptical ruptures using the derived characteristic rupture length and width. The semiautomated second moment method with seGfs can be used for routine application to moderate earthquakes in locations with good station coverage.