Highly heterogeneous pore fluid pressure enabled rupture of orthogonal
faults during the 2019 Ridgecrest Mw7.0 earthquake
Abstract
Here, we show that the 2019 Mw7.0 Ridgecrest mainshock as well as its
Mw6.5 foreshock ruptured orthogonal conjugate faults. We invert the
waveforms recorded by the dense strong-motion network at relatively high
frequencies (up to 1Hz for P, 0.25Hz for S) to derive multiple point
source models for both events, aided by path calibrations from a Mw5.4
earthquake. We demonstrate that the mainshock started from a shallow (3
km) depth with a Mw5.2 event, and ruptured the main fault branches
oriented in the NW-SE direction. At ~11 s, two Mw6.2
subevents took place on the SW-NE oriented fault branches that conjugate
to the main fault to the NE and SW. The SW branch rupture partially
overlapped with the foreshock rupture. We suggest the coseismic rupture
on nearly orthogonal faults was enabled by high pore fluid pressure,
which greatly weakened the immature fault system in a heterogeneous way.