Publications

The 40Ar/39Ar investigations of a large suite of fine-grained basaltic rocks of the Boring volcanic field (BVF), Oregon and Washington (USA), yielded two primary results. (1) Using age control from paleomagnetic polarity, stratigraphy, and available plateau ages, 40Ar/39Ar recoil model ages are defined that provide reliable age results in the absence of an age plateau, even in cases of significant

The 19 known shield volcanoes of the main Hawaiian Islands—15 now emergent, 3 submerged, and 1 newly born and still submarine—lie at the southeast end of a long-lived hot spot chain. As the Pacific Plate of the Earth’s lithosphere moves slowly northwestward over the Hawaiian hot spot, volcanoes are successively born above it, evolve as they drift away from it, and eventually die and subside beneat

We held 8 regional and topical workshops across the U.S. to gather information for these maps. The maps were available to the public for comment during a 60-day period. A Steering Committee (9 experts) was assembled to review the inputs and results and provide additional insights. The maps have been presented at several professional meetings.   In this talk we discuss:   (1) CEUS, (2) WUS (outside

Aseismic or slow slip events have been observed in many subduction zones, but whether they affect the occurrence of earthquakes or result from stress changes caused by nearby events is unclear. In an area lacking direct geodetic observations, inferences can be made from seismological studies of co-seismic slip, associated stress changes and the spatiotemporal nature of aftershocks. These observati

We estimate the arms‐stress drop, Graphic, (Hanks, 1979) using acceleration time records of 59 earthquakes from two earthquake sequences in eastern Honshu, Japan. These acceleration‐based static stress drops compare well to stress drops calculated for the same events by Baltay et al. (2011) using an empirical Green’s function (eGf) approach. This agreement supports the assumption that earthquake a

We present a quantitative procedure for constraining probabilistic seismic hazard analysis results at a given site, based on the existence of fragile geologic structures at that site. We illustrate this procedure by analyzing precarious rocks and undamaged lithophysae at Yucca Mountain, Nevada. The key metric is the probability that the feature would have survived to the present day, assuming that

Mazzotti and Adams (2004) estimated that rapid deep slip during typically two week long episodes beneath northern Washington and southern British Columbia increases the probability of a great Cascadia earthquake by 30–100 times relative to the probability during the ∼58 weeks between slip events. Because the corresponding absolute probability remains very low at ∼0.03% per week, their conclusion i

1] The Kanto seismic corridor surrounding Tokyo has hosted four to five M ≥ 7 earthquakes in the past 400 years. Immediately after the Tohoku earthquake, the seismicity rate in the corridor jumped 10-fold, while the rate of normal focal mechanisms dropped in half. The seismicity rate decayed for 6–12 months, after which it steadied at three times the pre-Tohoku rate. The seismicity rate jump and d

The Chilean tsunami of 22 May 1960 reamed out a breach and built up a fan as it flowed across a sparsely inhabited beach-ridge plain near Maullín, midway along the length of the tsunami source. Eyewitnesses to the flooding, interviewed mainly in 1988 and 1989, identified levels that the tsunami had reached on high ground, trees, and build- ings. The maximum levels fell, from about 10 m to 2 m, bet

This study focuses on the production of convergent margin calc-alkaline andesites by crystallization–differentiation of basaltic magmas in the lower to middle crust. Previous experimental studies show that dry, reduced, subalkaline basalts differentiate to tholeiitic (high Fe/Mg) daughter liquids, but the influences of H2O and oxidation on differentiation are less well established. Accordingly, we

A recent study by Schmidt et al. (2011) suggests that Thera Macula, one of the “chaos regions” on Europa, may be actively forming over a large liquid water lens. Such a process could conceivably produce a thermal anomaly detectable by a future Europa orbiter or flyby mission, allowing for a direct verification of this finding. Here, we present a set of models that quantitatively assess the surface

The complex tectonics surrounding the Philippine Islands are dominated by the interactions of the Pacific, Sunda, and Eurasia plates with the Philippine Sea plate (PSP). The latter is unique because it is almost exclusively surrounded by zones of plate convergence. At its eastern and southeastern edges, the Pacific plate is subducted beneath the PSP at the Izu-Bonin, Mariana, and Yap trenches. He