Monitoring time-dependent volcanic dynamics at Long Valley Caldera using InSAR and GPS measurements

Continuous monitoring Long Valley Caldera since the late 1970s, including data from seismic and geodetic networks has shown renewed episodic unrest activities with accelerated uplift separated by reduced uplift, no activity or slow deflation. We examine the time-dependent behaviors at Long Valley Caldera in 1996–2009 by integrating InSAR and continuous GPS (CGPS) measurements. The ERS-1/2 radar data between 1992 and 2008 and reprocessed three-component continuous GPS (CGPS) data from Long Valley GPS network in 1996–2009 were combined to invert for source geometry and volume change in the following deformation episodes: 97–98 uplift, 02–03 uplift, 04–07 slow subsidence, and 07–09 slow uplift. Our results show that all post-2000 events locate in the shallow depth range of ∼7–9 km and have nearly identical source location, suggesting that these events are caused by the same partial melt magma source at the mid-crustal level. All three events are characterized by the low volume change, in comparison with previous 1997–1998 inflation event that has much larger volume change and steeper source geometry. If we regard post-2000 events as proxy for future eruption hazard, the inferred source dynamics (e.g., mid-crustal location and low volume change) from these post-2000 events suggest that the probability for near-term eruption is low. Our study demonstrates that CGPS, along with InSAR, are important tools in monitoring time-dependent source process at the active volcano region.