Study of hydrological and volcanic processes at Long Valley Caldera, California, through GNSS data
École Normale Supérieure
Located at the eastern edge of Sierra Nevada range (SNR),Long Valley Caldera (LVC), California, experiences unrest episodes characterized by increased deformation and earthquake swarms. Furthermore, LVC is affected by hydrological deformation at different spatiotemporal scales controlled by the precipitation falling on SNR. Deformation measurements, such as from Global Navigation Satellite System (GNSS), therefore record superimposed effects of tectonic and non-tectonic processes. We analyze the deformation at LVC by combining GNSS and hydrological records. Vertical and horizontal components of GNSS displacement show a clear correlation with hydrological trends at both multiyear and seasonal time scales. At the seasonal timescale, deformation is largely controlled by the response to hydrological surface loading. However, several GNSS sites in the south/south-western rim of LVC show anomalous horizontal deformation. This is also where most of the recharging of the LVC hydrothermal system occurs and runoff-induced seismicity was identified. We show that the signal at these sites reflects poroelastic deformation in response to surface water recharge into SNR slopes. In 2011, the latest inflation episode began, while Western USA was affected byhighly variable climatic conditions with alternations of high precipitation and severe drought periods. We show the effect of this multiyear hydrological trend on the GNSS records in LVC. We apply a decomposition method to isolate inflation-related signals from the effect of this hydrological forcing. We finally invert inflation signals using a 3D numerical model to study the evolution of this inflation episode and assess the influence of topography and heterogeneous material properties.