Dilational Processes Accompanying Earthquakes in the Long Valley Caldera

Dreger, Douglas S.; Tkalčić, Hrvoje; Johnston, M. J. S.

doi:10.1126/science.288.5463.122

Cited by 169 publications

(121 citation statements)

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“…Over 24,000 recorded events occurred between January 1997 and February 1998 (Barton et al, 1999). Four of these had source solutions with statistically significant isotropic components (e.g., Dreger et al, 2000;Minson and Dreger, 2008). A comprehensive study of Long Valley seismicity confirmed the four unusual solutions and found one more event that had a resolvable isotropic component (Templeton and Dreger, 2006); however, most of the studied events were found to not deviate significantly from a pure DC solution.…”

Section: Introductionmentioning

confidence: 87%

“…Figure 2a shows the source-type plot for these 828 events distributed throughout northern California and The Geysers, denoted by plusses and circles, respectively. Dreger et al (2000) and Templeton and Dreger (2006) use the F-test to assess the statistical significance of the higher-degree-of-freedom full moment tensor solution compared with the lower-degree-of-freedom deviatoric solution. This test is based on the ratio of the model fit variance for the two cases normalized by the number of uncorrelated data.…”

Section: Statistical Comparison Of Northern California and The Geysermentioning

confidence: 99%

See 1 more Smart Citation

A Systematic Analysis of Seismic Moment Tensor at The Geysers Geothermal Field, California

Boyd¹,

Dreger²,

Lai³

et al. 2015

Bulletin of the Seismological Society of America

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The Geysers geothermal field is one of the most seismically active regions in northern California. Most of the events occur at shallow depths and are related to stress and hydrological perturbations due to energy production operations. To better understand the relationships between seismicity and operations, better source mechanism information is needed. Seismic moment tensors offer insight into the nature of equivalent forces causing the seismicity. Fifty-three M >3 events located at The Geysers geothermal field were selected from the University of California Berkeley Moment Tensor Catalog for analysis of seismic moment tensor solutions and associated uncertainties. Deviatoric and full moment tensor solutions were computed, and statistical tests were employed to assess solution stability, resolution, and significance. In this study, we examine several source models including double-couple (DC), pure isotropic (ISO; volumetric change), and volume-compensated linear vector dipole (CLVD) sources, as well as compound sources such as DC CLVD, DC ISO, and shear-tensile sources. In general, we find from a systematic approach toward characterizing uncertainties in moment tensor solutions that The Geysers earthquakes, as a population, deviate significantly from northern California seismicity in terms of apparent volumetric source terms and complexity.

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Section: Introductionmentioning

confidence: 87%

Section: Statistical Comparison Of Northern California and The Geysermentioning

confidence: 99%

A Systematic Analysis of Seismic Moment Tensor at The Geysers Geothermal Field, California

Boyd¹,

Dreger²,

Lai³

et al. 2015

Bulletin of the Seismological Society of America

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“…The Green's functions were computed using the FKRPROG software developed by Chandan Saikia of URS (Saikia, 1994). The deviatoric-and full-moment tensor solutions were calculated by applying a corrected form (Minson et al, 2007) of the linear time domain moment tensor inversion scheme used by Dreger et al (2000) and Dreger and Woods (2002). Moment tensors of the crack DC model were determined with a grid search algorithm developed and applied by Minson et al (2007).…”

Section: Moment Tensor Inversions Numerical Toolsmentioning

confidence: 99%

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Walter

Clinton²,

Deichmann³

et al. 2009

Bulletin of the Seismological Society of America

109

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We have determined seismic source mechanisms for shallow and intermediate-depth icequake clusters recorded on the glacier Gornergletscher, Switzerland, during the summers of 2004 and 2006. The selected seismic events are part of a large data set of over 80,000 seismic events acquired with a dense seismic network deployed in order to study the yearly rapid drainage of Gornersee lake, a nearby icemarginal lake. Using simple frequency and distance scaling and Green's functions for a homogeneous half-space, we calculated moment tensor solutions for icequakes with M w 1:5 using a full-waveform inversion method usually applied to moderate seismic events (M w > 4) recorded at local to regional distances (≈50-700 km). Inversions from typical shallow events are shown to represent tensile crack openings. This explains well the dominating Rayleigh waves and compressive first motions observed at all recording seismograms. As these characteristics can be observed in most icequake signals, we believe that the vast majority of icequakes recorded in the 2 yr is due to tensile faulting, most likely caused by surface crevasse openings. We also identified a shallow cluster with somewhat atypical waveforms in that they show less dominant Rayleigh waves and quadrantal radiation patterns of first motions. Their moment tensors are dominated by a large double-couple component, which is strong evidence for shear faulting. Although less than a dozen such icequakes have been identified, this is a substantial result as it shows that shear faulting in glacier ice is generally possible even in the absence of extreme flow changes such as during glacier surges. A third source of icequakes was located at 100 m depth. These sources can be represented by tensile crack openings. Because of the high-hydrostatic pressure within the ice at these depths, these events are most likely related to the presence of water lenses that reduce the effective stress to allow for tensile faulting.Online Material: Background information and results of moment tensor inversions.

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“…Earthquake swarms are mainly attributed to volcanic areas, geothermal fields, and mid-ocean rifts (e.g. Wyss et al, 1997;Dreger et al, 2000), the worldwide most intensive swarms occur apparently in Iceland, which is a part of the mid-Atlantic plate boundary (e.g. Stefansson et al, 2006, Jakobsdóttir et al, 2008.…”

Section: Introductionmentioning

confidence: 99%

The 2008 West Bohemia earthquake swarm in the light of the WEBNET network

et al. 2010

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International audienceA swarm of earthquakes of magnitudes up to = 3.8 stroke the region of West Bohemia/Vogtland (border area between Czechia and Germany) in October 2008. It occurred in the Nový Kostel focal zone, where also all recent earthquake swarms (1985/1986, 1997, and 2000) took place, and was striking by a fast sequence of macroseismically observed earthquakes. We present the basic characteristics of this swarm based on the observations of a local network WEBNET (West Bohemia seismic network), which has been operated in the epicentral area, on the Czech territory. The swarm was recorded by 13 to 23 permanent and mobile WEBNET stations surrounding the swarm epicenters. In addition, a part of the swarm was also recorded by strong-motion accelerometers, which represent the first true accelerograms of the swarm earthquakes in the region. The peak ground acceleration reached 0.65 m/s. A comparison with previous earthquake swarms indicates that the total seismic moments released during the 1985/1986 and 2008 swarms are similar, of about 4E16 Nm, and that they represent the two largest swarms that occurred in the West Bohemia/ Vogtland region since the = 5.0 swarm of 1908. Characteristic features of the 2008 swarm are its short duration (4 weeks) and rapidity and, consequently, the fastest seismic moment release compared to previous swarms. Up to 25,000 events in the magnitude range of 0.5 < < 3.8 were detected using an automatic picker. A total of nine swarm phases can be distinguished in the swarm, five of them exceeding the magnitude level of 2.5. The magnitude-frequency distribution of the complete 2008 swarm activity shows a value close to 1. The swarm hypocenters fall precisely on the same fault portion of the Nový Kostel focal zone that was activated by the 2000 swarm ( ≤ 3.2) in a depth interval from 6 to 11 km and also by the 1985/1986 swarm ( ≤ 4.6). The steeply dipping fault planes of the 2000 and 2008 swarms seem to be identical considering the location error of about 100 m. Furthermore, focal mechanisms of the 2008 swarm are identical with those of the 2000 swarm, both matching an average strike of 170° and dip of 80° of the activated fault segment. An overall upward migration of activity is observed with first events at the bottom and last events at the top of the of the activated fault patch. Similarities in the activated fault area and in the seismic moments released during the three largest recent swarms enable to estimate the seismic potential of the focal zone. If the whole segment of the fault plane was activated simultaneously, it would represent an earthquake of ~5. This is in good agreement with the estimates of the maximum magnitudes of earthquakes that occurred in the West Bohemia/Vogtland region in the past

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Dilational Processes Accompanying Earthquakes in the Long Valley Caldera

Cited by 169 publications

References 20 publications

A Systematic Analysis of Seismic Moment Tensor at The Geysers Geothermal Field, California

A Systematic Analysis of Seismic Moment Tensor at The Geysers Geothermal Field, California

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

The 2008 West Bohemia earthquake swarm in the light of the WEBNET network

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