David Hill (Former Employee)
Science and Products
Post-1978 tumescence at Long Valley Caldera, California: A geophysical perspective
Long Valley Caldera has been restless since at least 1978. Prominent symptoms of this unrest include earthquake swarms and tumescence (inflation) centered on the resurgent dome. Over the years, interpretations of physical processes underlying this unrest have varied considerably. Results from a collection of geophysical studies infer the presence...
Hill, David P.; Montgomery-Brown, Emily; Shelly, David R.; Flinders, Ashton; Prejean, Stephanie Deep fluid pathways beneath Mammoth Mountain, California, illuminated by migrating earthquake swarms
Although most volcanic seismicity is shallow (within several kilometers of the surface), some volcanoes exhibit deeper seismicity (10 to 30+ km) that may reflect active processes such as magma resupply and volatile transfer. One such volcano is Mammoth Mountain, California, which has also recently exhibited high rates of CO2 discharge at the...
Hotovec-Ellis, Alicia J.; Shelly, David R.; Hill, David P.; Pitt, Andrew M.; Dawson, Phillip B.; Chouet, Bernard A. Seismic evidence for significant melt beneath the Long Valley Caldera, California, USA
A little more than 760 ka ago, a supervolcano on the eastern edge of California (United States) underwent one of North America's largest Quaternary explosive eruptions. Over this ~6-day-long eruption, pyroclastic flows blanketed the surrounding ~50 km with more than 1400 km3 of the now-iconic Bishop Tuff, with ashfall reaching as far east as...
Flinders, Ashton; Shelly, David R.; Dawson, Phillip B.; Hill, David P.; Tripoli, Barbara; Shen, Yang Volcanic unrest and hazard communication in Long Valley Volcanic Region, California
The onset of volcanic unrest in Long Valley Caldera, California, in 1980 and the subsequent fluctuations in unrest levels through May 2016 illustrate: (1) the evolving relations between scientists monitoring the unrest and studying the underlying tectonic/magmatic processes and their implications for geologic hazards, and (2) the challenges in...
Hill, David P.; Mangan, Margaret T.; McNutt, Stephen R. Long Valley Caldera-Mammoth Mountain unrest: The knowns and the unknowns
This perspective is based largely on my study of the Long Valley Caldera (California, USA) over the past 40 years. Here, I’ll examine the “knowns” and the “known unknowns” of the complex tectonic–magmatic system of the Long Valley Caldera volcanic complex. I will also offer a few brief thoughts on the “unknown unknowns” of this system.
Hill, David P. Fluid-faulting interactions: Fracture-mesh and fault-valve behavior in the February 2014 Mammoth Mountain, California, earthquake swarm
Faulting and fluid transport in the subsurface are highly coupled processes, which may manifest seismically as earthquake swarms. A swarm in February 2014 beneath densely monitored Mammoth Mountain, California, provides an opportunity to witness these interactions in high resolution. Toward this goal, we employ massive waveform-correlation-based...
Shelly, David R.; Taira, Taka’aki; Prejean, Stephanie; Hill, David P.; Dreger, Douglas S. S-wave triggering of tremor beneath the Parkfield, California, section of the San Andreas fault by the 2011 Tohoku, Japan earthquake: observations and theory
The dynamic stresses that are associated with the energetic seismic waves generated by the Mw 9.0 Tohoku earthquake off the northeast coast of Japan triggered bursts of tectonic tremor beneath the Parkfield section of the San Andreas fault (SAF) at an epicentral distance of ∼8200 km. The onset of tremor begins midway through the ∼100‐s‐period S‐...
Hill, David P.; Peng, Zhigang; Shelly, David R.; Aiken, Chastity Dynamic stresses, Coulomb failure, and remote triggering
Dynamic stresses associated with crustal surface waves with 15-30-sec periods and peak amplitudes < 1 MPa are capable of triggering seismicity at sites remote from the generating mainshock under appropriate conditions. Coulomb failure models based on a frictional strength threshold offer one explanation for instances of rapid-onset triggered...
Hill, David P. Very-long-period volcanic earthquakes beneath Mammoth Mountain, California
Detection of three very‐long‐period (VLP) volcanic earthquakes beneath Mammoth Mountain emphasizes that magmatic processes continue to be active beneath this young, eastern California volcano. These VLP earthquakes, which occurred in October 1996 and July and August 2000, appear as bell‐shaped pulses with durations of one to two minutes on a...
Hill, David P.; Dawson, P.; Johnston, M. J. S.; Pitt, A. M.; Biasi, G.; Smith, K.