David A. Schmidt

Time-dependent land uplift and subsidence in the Santa Clara valley, California, from a large interferometric synthetic aperture radar data set

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Slicing up the San Francisco Bay Area: Block kinematics and fault slip rates from GPS‐derived surface velocities

Received 26 October 2004; revised 11 February 2005; accepted 10 March 2005; published 16 June 2005. [i] Observations of surface deformation allow us to determine the kinematics of faults in the San Francisco Bay Area. We present the Bay Area velocity unification (BAVU, bay view), a compilation of over 200 horizontal surface velocities computed from campaign-style and continuous Global Positioning System (GPS) observations from 1993 to 2003. We interpret this interseismic velocity field using a three-dimensional block model to determine the relative contributions of block motion, elastic strain accumulation, and shallow aseismic creep. The total relative motion between the Pacific plate and the rigid Sierra Nevada/Great Valley (SNGV) microplate is 37.9 ± 0.6 mm yr -1 directed toward N30.4°W ± 0.8° at San Francisco (±2σ). Fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data (notable right-lateral slip rates in mm yr -1 : San Gregorio fault, 2.4 ± 1.0; West Napa fault, 4.0 ± 3.0; zone of faulting along the eastern margin of the Coast Range, 5.4 ± 1.0; and Mount Diablo thrust, 3.9 ± 1.0 of reverse slip and 4.0 ± 0.2 of right-lateral strike slip). Slip on the northern Calaveras is partitioned between both the West Napa and Concord/Green Valley fault systems. The total convergence across the Bay Area is negligible. Poles of rotation for Bay Area blocks progress systematically from the North America-Pacific to North America-SNGV poles. The resulting present-day relative motion cannot explain the strike of most Bay Area faults, but fault strike does loosely correlate with inferred plate motions at the time each fault initiated.

Landslides, threshold slopes, and the survival of relict terrain in the wake of the Mendocino Triple Junction

Establishing landscape response to uplift is critical for interpreting sediment fluxes, hazard potential, and topographic evolution. We assess how landslides shape terrain in response to a wave of uplift traversing the northern California Coast Ranges (United States) in the wake of the Mendocino Triple Junction. We extracted knickpoints, landslide erosion rates, and topographic metrics across the region modified by Mendocino Triple Junction migration. Landslide erosion rates mapped from aerial imagery are consistent with modeled uplift and exhumation, while hillslope gradient is invariant across the region, suggesting that landslides accommodate uplift, as predicted by the threshold slope model. Landslides are concentrated along steepened channel reaches downstream of knickpoints generated by base-level fall at channel outlets, and limit slope angles and relief. We find evidence that landslide-derived coarse sediment delivery may suppress catchment-wide channel incision and landscape denudation over the time required for the uplift wave to traverse the region. We conclude that a landslide cover effect may provide a mechanism for the survival of relict terrain and orogenic relief in the northern Californian Coast Ranges and elsewhere over millennial time scales.

Historic drought puts the brakes on earthflows in Northern California

Californias ongoing, unprecedented drought is having profound impacts on the states resources. Here we assess its impact on 98 deep-seated, slow-moving landslides in Northern California. We used aerial photograph analysis, satellite interferometry, and satellite pixel tracking to measure earthflow velocities spanning 1944–2015 and compared these trends with the Palmer Drought Severity Index, a proxy for soil moisture and pore pressure that governs landslide motion. We find that earthflow velocities reached a historical low in the 2012–2015 drought, but that their deceleration began at the turn of the century in response to a longer-term moisture deficit. Our analysis implies depth-dependent sensitivity of earthflows to climate forcing, with thicker earthflows reflecting longer-term climate trends and thinner earthflows exhibiting less systematic velocity variations. These findings have implications for mechanical-hydrologic interactions that link landslide movement with climate change as well as sediment delivery in the region.

Deep long-period earthquakes west of the volcanic arc in Oregon: evidence of serpentine dehydration in the fore-arc mantle wedge

Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction fore arc: 40–80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likely to be serpentinized and cold. The lack of fore-arc DLPs elsewhere along the arc suggests that localized heating may be dehydrating the serpentinized mantle wedge at these latitudes and causing DLPs by dehydration embrittlement. Higher heat flow in this region could be introduced by anomalously hot mantle, associated with the western migration of volcanism across the High Lava Plains of eastern Oregon, entrained in the corner flow proximal to the mantle wedge. Alternatively, fluids rising from the subducting slab through the mantle wedge may be the source of offset DLPs. As far as we know, these are among the first DLPs to be observed in the fore arc of a subduction-zone system.

Long-term deformation of slow moving landslides in the Northern Apennines of Italy imaged by SAR interferometry

Slow moving earth-flows are a common geomorphological feature in the Northern Apennines and one of the main landscape forming agents. Often houses and small villages were built on these phenomena which are as consequence affected by damages that are caused by small displacements. In this short note, we present the InSAR results obtained from the Stanford Method of Persistent Scatterers (StaMPS) for Cosmo SkyMed and Envisat imagery together with a geological-geomorphological survey. We focus on the village of Gaggio Montano located in the Apennines south of Bologna. Here the tectonically sheared Flysch of the Monghidoro Formation structurally overlies the melange of the Palombini shales and different complex landslides were mapped on the slope. We show that several landslide bodies are moving with steady deformation rates at least since 2003 and that the results obtained from Envisat and Cosmo SkyMed compare well to each other. Moreover the displacements measured by InSAR are in the same order of magnitude as displacements that have been measured in the past with inclinometers. Because the higher deformation rates are closely related to young houses and industrial complexes, it is possible that anthropogenic factors, like leakage from the water supply/discharge system, influence the displacements. A steady infiltration of water from the Flysch slabs into the clay shales might however represent a possible explanation

Development of a Geodetic Component for the U.S. West Coast Earthquake Early Warning System

An earthquake early warning (EEW) system, ShakeAlert, is under development for the West Coast of the United States. This system currently uses the first few seconds of waveforms recorded by seismic instrumentation to rapidly characterize earthquake magnitude, location, and origin time; ShakeAlert recently added a seismic line source algorithm. For large to great earthquakes, magnitudes estimated from the earliest seismic data alone generally saturate. Real-time Global Navigation Satellite System (GNSS) data can directly measure large displacements, enabling accurate magnitude estimates for Mw7 events, possibly before rupture termination. GNSS-measured displacements also track evolving slip and, alone or in combination with seismic data, constrain finite-fault models. Particularly for large-magnitude, long-rupture events, GNSS-based magnitude and rupture extent estimates can improve updates to predicted shaking and thus alert accuracy. GNSS data processing centers at ShakeAlert partner institutions provide real-time streams to the EEWsystem, and three geodetic EEW algorithms have been developed through the ShakeAlert collaboration. These algorithms will undergo initial testing within ShakeAlert’s computational architecture using a suite of input data that includes simulated real-time displacements from synthetic earthquakes and GNSS recordings from recent earthquakes worldwide. Performance will be evaluated using metrics and standards consistent with those adopted for ShakeAlert overall. This initial assessment will guide method refinement and synthesis of the most successful features into a candidate geodetic algorithm for the ShakeAlert production system. In parallel, improvements to geodetic networks and streamlining approaches to data processing and exchange will ensure robust geodetic data availability in the event of an earthquake. Electronic Supplement: Table listing recent earthquakes for which high sample-rate (≥ 1 Hz) processed Global Positioning System data and seismic data have been gathered for use in testing geodetic earthquake early warning algorithms and a summary of ground-motion metrics adopted by ShakeAlert, the U.S. West Coast EEW system, for evaluating new or updated components before adoption in the production system, and a schematic diagram of the real-time Global Navigation Satellite Systems data flow for ShakeAlert.

Designing an offshore geophysical network in the Pacific Northwest for earthquake and tsunami early warning and hazard research

Every few hundred years, the Cascadia subduction zone off the coast of the Pacific Northwest hosts devastating earthquakes, and there is a growing awareness of the need to be prepared for these events. An offshore cabled observatory extending the length of the Cascadia subduction zone would enhance the performance of the earthquake and tsunami early warning systems, would enable real time monitoring and predictions of the incoming tsunami, and would contribute substantially to scientific research aimed at mitigating the hazard. The University of Washington has recently initiated a study to develop a conceptual design for the U.S. portion of an offshore observatory for earthquake and tsunami early warning and research. This paper presents the motivation for this work and plans for the study.