A study by Tizzani et al. provides compelling evidence that magma is forcing Long Valley caldera, located in the east side of the Sierra Nevada in Central California, upward. The caldera has been the site of major geologic unrest in the past 33 years, characterized by 75 cm of uplift of the resurgent dome in the central section of the caldera, and earthquake activity followed by periods of relative quiescence. Tizzani et al. investigate the cause of unrest by a joint inversion of surface deformation measurements, based on differential synthetic aperture radar interferometry (InSAR), and microgravity data. The critical convergence of geodetic and microgravity data require a local mass increase beneath the resurgent dome consistent with magma intrusion, contributing to the two decades of Long Valley caldera unrest from 1980 through early 2000.
Pore-pressure migration along a normal-fault system resolved by time-repeated seismic tomography
Claudio Chiarabba et al., Istituto Nazionale di Geofisica e Vulcanologia, via di Vigna Murata 605, 00143 Rome, Italy. Pages 67-70.
In this study, Chiarabba et al. outline the space and time variations of body wave velocities which occurred during one of the best-documented series of normal faulting earthquakes, the 1997 Umbria-Marche sequence in central Italy. They show the first ever observations of rock fracturing and fluid overpressure propagation along a fault system by using space-time resolved variations of Vp/Vs anomalies (4D variations), which accompany earthquake migration and precede large aftershocks. The Vp/Vs increase observed before the mid-October earthquakes is related to a pore pressure increase on fluid-filled cracks in the volume around the fault. Chiarabba et al. also document that such variations are measurable by only using S- and P-wave arrival times.
Is there a link between Earth's m
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Geological Society of America