Snowmelt-Triggered Earthquake Swarms at the Margin of Long Valley Caldera, California

Date: 4/26/2019

Time: 04:45 PM

Room: Cascade I

Fluids are known to influence earthquakes, yet rarely are earthquakes convincingly linked to precipitation. Weak modulation or limited data often leads to ambiguous interpretations. In contrast, we found that shallow seismicity in the Sierra Nevada range near Long Valley Caldera is strongly modulated. Over 33 years, shallow seismicity rates were ~37 times higher during very wet periods versus very dry periods. Precise earthquake locations from a swarm in 2017 reveal downward migration from ~1-3 km depth along a steeply inclined plane. Steeply dipping strata may provide high-permeability pathways and faulting plane. Here we combine the correlated seismicity and hydrologic time series with the propagation observed in the relocated earthquakes. From this combined evidence, we infer that pressure diffusion from groundwater recharge dramatically accelerated shallow seismicity rates, causing seismic swarms unrelated to volcanic processes. The observed deformation helps differentiate timing and effects solely due to the load of the winter snowfall, from those of the later infiltration of meltwater.

Presenting Author: Emily Montgomery-Brown

Authors