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

Abstract

Fluids are well known to influence earthquakes, yet rarely are earthquakes convincingly linked to precipitation. Weak modulation or limited data often leads to ambiguous interpretations. In contrast, here we find that shallow seismicity in the Sierra Nevada range near Long Valley Caldera is strongly modulated by snowmelt. Over 33 years, shallow seismicity rates were ~37 times higher during very wet periods versus very dry periods. Relative earthquake relocations from a swarm in 2017 reveal downward migration from ~1‐ to 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 relatively 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.

Hydrologically Induced Deformation in Long Valley Caldera and Adjacent Sierra Nevada

“…This mechanism could be responsible for the observed alternating pattern of rapid outward and slower inward motion at GNSS stations on the southwestern rim of LVC. In this interpretation, the amplitude of the horizontal deformation would correlate with the amplitude of seasonal groundwater‐level fluctuations (<2 m in dry years and >10 m in wet years, Montgomery‐Brown et al, ) and the deformation would preferentially occur in typically highly fractured areas around the caldera (Acocella, ; Walter & Motagh, ; Wang et al, ). Interestingly, the largest horizontal amplitude occurs at station MINS, which moves in southwest direction in spring/summer and lies on the west side of Mammoth Mountain, one of the main infiltration areas of LVC hydrothermal system (Pribnow et al, ; Peacock et al, ).…”

“…All raw data are available from public databases: GNSS data are available at the USGS website (https://earthquake.usgs.gov/monitoring/gps/stations), precipitation and temperature data at the NOAA website (https://www.ncdc.noaa.gov/cdo-web), stream discharge data at the USGS National Water Information System website (https://waterdata.usgs.gov/ca/nwis), and lakes level data at the following sites (https://www.monolake.org/today/water, https://maps.waterdata.usgs.gov/, and https://cdec.water.ca.gov/cdecstation2/?sta=BIS). The Convict Lake swarm seismicity data are from Montgomery‐Brown et al () and based on the catalog data of the Northern California Earthquake Data Center (doi:10.7932/NCEDC). Figures have been produced by using the Generic Mapping Tools (GMT) software (Wessel et al, ) and MATLAB software.…”

“…LVC is impacted by precipitation falling on the adjacent SNR. Its diffuse hydrothermal system is recharged mainly from snowmelt along the western/southwestern caldera rim (Peacock et al, 2016;Sorey et al, 1991), 10.1029/2020JB019495 and SNR runoff has been linked to the occurrence of shallow earthquake swarms on the caldera margin (Montgomery-Brown et al, 2019). Furthermore, a recent study suggested a correlation between SNR unloading due to the recent 2012-2016 drought and the most recent inflation episode at LVC (Hammond et al, 2019).…”

Potential Link Between 2020 Mentone, West Texas M5 Earthquake and Nearby Wastewater Injection: Implications for Aquifer Mechanical Properties

“…Therefore, a small perturbation of the stress field due to fluid diffusion can likely trigger earthquakes. Some examples include seasonal modulation of the seismicity due to hydrological unloading (Carlson et al, 2020;Christiansen et al, 2007;Johnson et al, 2017), triggering earthquakes due to tides (Tanaka et al, 2002;Wilcock, 2001) and induced seismicity due to pore-pressure change by seasonal snowmelt (Montgomery-Brown et al, 2019;Saar & Manga, 2003). Several studies suggested that a pore-pressure increase of 0.01-0.1 MPa can trigger seismicity (Harris, 1998;Roeloffs, 1996;Stein et al, 1992Stein et al, , 1994.…”

Earthquake Hydrogeology

“…Seismicity induced by wastewater disposal in the U.S. midcontinent is one example (e.g., Ellsworth, ). In a recent and dramatic natural example, shallow seismicity in the Sierra Nevada near Long Valley Caldera, California—a high‐threat volcanic area—was shown to be strongly modulated by snowmelt, with seismicity rates ~37 times higher during very wet periods versus very dry periods (Montgomery‐Brown et al, ).…”