Stress drop validation and triggering process of foreshocks in Southern
Earthquake stress drop is an important source parameter that directly
links to strong ground motion. However, estimating stress drops is often
challenging due to many factors, such as data limitations, methodology,
and attenuation. Different studies may yield highly inconsistent stress
drop values for the same earthquakes, leading to different
interpretations of stress drop scaling and spatial patterns. Stress drop
is also important for interpretation of earthquake triggering processes.
In particular, the roles of foreshocks have continuous debate, and some
recent studies show that detailed source parameter analysis is the key.
In this study, we combine analyses of three sequences in Southern
California using different methods to investigate the resolution of
stress drops and the roles of foreshocks. The three sequences include
the M7 El-Mayor Cucapah, the 2012 M5 Brawley swarm, and the 2019 M7
Ridgecrest sequence. The Ridgecrest sequence will participate in the
Community Stress Drop Validation Study. For each sequence, we apply an
improved stacking method and a spectral ratio method. We will use
different types of waves: P-wave, S-wave, and Coda-wave. Stress drop
results from this study will be compared with available previous
studies. We will first discuss the influence of wave type and
methodology on stress drop estimations, then we will investigate
detailed stress interactions between foreshocks and the mainshock for
different types of earthquake sequences (i.e., mainshock-aftershock and
swarms that involve aseismic slip or fluid).