Spatial variations of rock damage production by earthquakes in southern California

We perform a comparative spatial analysis of inter-seismic earthquake production of rupture area and volume in southern California using observed seismicity and basic scaling relations from earthquake phenomenology and fracture mechanics. The analysis employs background events from a declustered catalog in the magnitude range 2 <= M < 4 to get temporally stable results representing activity during a typical inter-seismic period on all faults. Regions of high relative inter-seismic damage production include the San Jacinto fault, South Central Transverse Ranges especially near major fault junctions (Cajon Pass and San Gorgonio Pass), Eastern CA Shear Zone (ECSZ) and the Imperial Valley - Brawley seismic zone area. These regions are correlated with low velocity zones in detailed tomography studies. A quasi-linear zone with ongoing damage production extends between the Imperial fault and ECSZ and may indicate a possible future location of the main plate boundary in the area. The regions around the 1992 M6.1 Joshua Tree, M7.3 Landers and M6.3 Big Bear earthquakes have background seismic activity before 1990. This may represent a regional weakening process by damage production in future rupture zones. The depth of background seismicity and damage production decreases steadily from SW of the coastline to NE of the San Andreas fault, and also to the SE near the US-Mexico border. The seismicity and rock damage become more pronounced and continuous along-strike of main faults with increasing depth. (C) 2019 Elsevier B.V. All rights reserved.