Renewed Inflation of Long Valley Caldera (2011 – Present)

Abstract:

Slow inflation resumed at Long Valley Caldera in late 2011, coinciding with renewed south moat swarm activity. Deformation is predominantly concentrated within the caldera, but a small amplitude spatially-coherent deformation extends northward to Mono Lake, suggesting the influence of multiple deformation sources. Small deviations from the nearly steady inflation are observed during the winter months. The frequency of earthquake swarms has also increased during the renewed inflation, with earthquakes occurring at about 8 km depth. While the majority of the increased seismicity occurring during the inflation can be explained by a single earthquake triggering model (e.g., Epidemic Type Aftershock Sequence), swarms occurring during the seasonal deviations observed by GPS are not well fit by this model. To study the renewed inflation, we analyze long term trends and transient deformation in GPS and InSAR data in the context of seismic and meteorological observations. InSAR data are from X-band (3.11 cm wavelength) radar satellites Terrasar-X and Tandem-X. We process initial interferograms using GAMMA, and process persistent scatterers (PS) using DORIS and StaMPS with both the multi-temporal and small baseline pair methods. PS coverage is very good and StaMPS identifies over 5 million PS, which we downsample to a spacing of 200 m for efficiency. The extension rate of the dome-crossing baseline (CA99 to KRAC) is ~1 cm/yr, similar to rates observed in previous inflation episodes (1990-95 and 2002-03), which is about a tenth of the peak rate observed during the late 1997 unrest. The current deformation can be explained by the inflation of a nearly spherical magma reservoir at ~6 km deep beneath the resurgent dome, with a volume change of ~4.5(±1)x10⁶ m³/yr. This source appears to be in a region that was used to model previous inflation episodes. A deeper source at 12 km, used to help model the 1997 inflation may contribute to the current deformation.