Constraints on continued episodic inflation at Long Valley Caldera, based on seismic and geodetic observations

Abstract

Long Valley Caldera, a large and potentially explosive silicic system, has experienced highly anomalous continued inflation since late 1970s. We characterize an episode of rapid episodic uplift occurring between 2002 and 2003 following similar episodes of 1979–1980, 1983, 1989–1990, and 1997–1998. This most recent episode was the first to be observed by a dense array of 13 continuous Global Positioning System (GPS) stations. Similar to previously observed episodes of deformation, uplift is quasi‐radially symmetric and is mostly explained by a compact pressure source located ∼3 km west of the resurgent dome. The maximum uplift during the 2002–2003 episode is ∼35 ± 8 mm, about 1/3 the magnitude but with a similar time‐dependent behavior as the 1997–1998 episode. The horizontal source location is well constrained at −118.930°, 37.678°, for a small spherical source, and indistinguishable from the location of a vertically dipping prolate spheroidal source. A trade‐off between depth and volume change is observed for both spherical and prolate models, with depth between 7.5 and 13.5 km and a volume change of 0.01–0.03 km3 at 95% confidence. For prolate spheroidal models, depth and volume change are additionally affected by the source axis ratio (b/a), which is greater than 0.55. Though the background seismicity remained low during the 2002–2003 episode, we identified a significant spike in activity during the maximum rate of uplift, similar to observations in both the much larger episodes in 1989–1990, and 1997–1998. More interestingly, we additionally find that all three episodes begin immediately after a short period of seismic quiescence, with background seismicity falling to levels below background levels following the prior uplift event. With the dense GPS coverage, we also identify increased opening of the Mono‐Inyo volcanic chain after the 2002–2003 episode suggesting potential interaction of magmatic fluids between the two systems.

Recent geodetic unrest at Santorini Caldera, Greece

“…[13] As seen in other active silicic calderas, including Long Valley [Newman et al, 2006;Feng and Newman, 2009] and Yellowstone [Chang et al, 2007], and the recently erupting Eyjafjallajökull stratovolcano [Sigmundsson et al, 2010], the temporal occurrence of seismicity mimics observed deformation (Figure 1). Each change in the cumulative seismicity marks a similar change in the rate of deformation.…”

“…Such a model requires only the assumption that a small spherical source is radially expanding in a homogeneous elastic Poisson half-space. Following an iterative grid search method used by Feng and Newman [2009], we use an apriori estimate of DV and depth z to initially constrain a preferred horizontal position. Using this position a new best fit z and DV is determined, which are again used as input for a repeated grid search to refine the location and DV for improved final solutions.…”

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

“…Previous studies on the 1997-1998, 2002-2003 uplift events indicate that the intrusion beneath the resurgent dome may be cigar-shaped [e.g., 10,11,12,13]. So we assume the most recent deformation episodes since 2000 are caused similarly by a finite ellipsoidal source.…”

Adjustment of highly non-linear redundant systems of equations using a numerical, topology-based approach

“…This may seem peculiar, if not paradoxal, at least for the cases of geodetic data describing geophysical models; for instance modeling seismic faults from comparison of preand post-seismic geodetic observations [5,8,12] and modeling of magma sources in volcanoes from comparison of GPS or INSAR data from different campaigns [4,11].…”