Open AccessMapping asperities by minima of local recurrence time: San Jacinto‐Elsinore fault zones
Author(s) -
Wyss Max,
Schorlemmer Danijel,
Wiemer Stefan
Publication year - 2000
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jb900347
Subject(s) - maxima and minima , geology , maxima , fault (geology) , asperity (geotechnical engineering) , seismology , range (aeronautics) , magnitude (astronomy) , geodesy , geometry , physics , mathematics , astrophysics , materials science , art , mathematical analysis , geotechnical engineering , performance art , composite material , art history
Minima of the local recurrence time, T L ( M ), are correlated with the locations of historical main shocks in the San Jacinto (SJ)‐Elsinore (E) fault zones of southern California. We define T L ( M ) as the recurrence time calculated from the local b and a values of the frequency‐magnitude distribution (earthquakes within 6 and 10 km from each point in the SJ and E fault zones, respectively). We propose that anomalously low T L ( M ) values map asperities. Out of six historic main shocks (1899–1968), five ruptured substantial parts of four asperities mapped by our method, which uses solely the modern earthquake catalog ( M ≥ 1.2, 1981.0–1998.8). We estimate the probability for this correlation to occur at random as ∼10 −2 to 10 −3 , depending on the scenario chosen. It appears that the minima in T L ( M ) are tied to minima in b values more than to maxima in a values. Thus locations of low b values can also be used as an indication where asperities may be located and where main shocks are most likely. The Anza gap, a segment of the San Jacinto fault with low a values, is mapped as an asperity by our method. The heterogeneity in b values is strong throughout the study area. The b values range from 0.5 to 1.8 over distances of 10 km. Volumes with approximately constant b values have radii of r = 8±6 km. Our results suggest that detailed mapping of b values and local recurrence times in volumes with a few kilometers radius reveals important information about the local seismic hazard, hitherto untapped by conventional seismicity analyses.