Dynamic triggering of earthquakes is when seismic waves from earthquakes induce seismic activity at a distance. The observability of the seismic wave stresses and their results presents a unique opportunity to understand earthquake interactions and associated hazard implications. The extent and timing of dynamic triggering at given specific stress changes still remain inadequately predicted due to limited studies and datasets. In particular, the requirement for complete, well-characterized catalogs to detect triggering systematically seriously limits the types of studies possible. To address this, we utilized 7-year continuous waveform data from 239 stations in southern California and used PhaseNet for phase picking to identify local earthquakes and measure triggering without constructing any earthquake catalog. We map the triggering intensity over the region and find that overall, the Mojave segment of the San Andreas is the most easily triggered region. However, the spatial pattern changes after the Ridgecrest earthquake and the area becomes much less prone to triggering, likely due to an exhaustion of the faults near failure in the immediate aftermath of the Ridgecrest sequence. We further observe a slow decay rate of dynamic triggering and conclude that low-frequency waves (0.04-0.1 Hz) may be more effective in dynamic triggering than high-frequency waves (1-3 Hz) which is consistent with a rate-state assisted aseismic creep or hydrological triggering mechanism.

A document by Alba Mar Rodriguez Padilla. Click on the document to view its contents.

Variations in fault maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between field measurements indicative of fault zone maturity and remotely measured seismological source parameters of 34 large shallow strike-slip events. Metrics based on fault segmentation, such as number of primary rupture segments and surface rupture azimuth, correlate best with seismic source attributes and the correlations with cumulative fault slip are somewhat weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment-scaled radiated energy. There appears to be distinct behavior of very immature events with no prior mapped fault and < 1 km cumulative slip, which radiate modest seismic energy, while moderately mature faults have events with higher moment-scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reducing moment-scaled radiated energy. We also explore qualitative and composite assessments of maturity and arrive at similar trends. This empirical approach establishes that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of blind fault systems for which direct observations of maturity are very limited.