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Yuehua Zeng - One of the best experts on this subject based on the ideXlab platform.
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viscoelastic stress triggering of the 1999 hector mine earthquake by the 1992 landers earthquake
Geophysical Research Letters, 2001Co-Authors: Yuehua ZengAbstract:The 1999 Mw 7.1 Hector Mine earthquake occurred only 20 km from the 1992 Mw 7.3 Landers earthquake fault. The close spacing between the two earthquakes suggests that the Landers earthquake trigger the Hector Mine event. Based on an elastic half-space model, scientists from the USGS, SCEC and CDMG (2000) have found a negative Coulomb stress change at the Hector Mine hypocenter due to Landers. This negative stress change is inconsistent with the hypothesis of static stress triggering. In this paper, I show evidence of stress triggering of the Hector Mine earthquake by Landers, due to a process governed by viscoelastic flow in the lower crust. This visoelastic flow has produced broad-scale postseismic rebound observed by GPS and InSAR measurements. The result of this study is that viscoelastic flow has significantly modified the regional stress field in the Mojave Desert after the Landers earthquake. The evolving stress field, including viscoelastic flow, has gradually moved the Coulomb stress change at the Hector Mine hypocenter to a positive level. The increase in Coulomb stress exceeded 1 bar right before the Hector Mine earthquake, bringing the Hector Mine ruptures to the proximity of catastrophic failure.
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seismicity in the western great basin apparently triggered by the landers california earthquake 28 june 1992
Bulletin of the Seismological Society of America, 1994Co-Authors: John G Anderson, James N Brune, John N Louie, Yuehua Zeng, Martha K Savage, Qingbin Chen, Diane DepoloAbstract:Within 24 hr after the Landers earthquake, there were three magnitude 3.4+ events in western Nevada and an unexpected, widespread increase in the rate of small events. Based on combined catalogs for northern Nevada, southern Nevada, and southern California, and a model that assumes statistical independence of events in these regions, the probability of this happening in a 24-hr period by random chance is less than ∼10−12 per day. Therefore, there is high statistical confidence that the increased seismicity was triggered by the Landers event. Based on the statistical model, we develop a list of 227 earthquakes in the first 83 days following the Landers earthquake, each of which has no more than 10% probability of occurring by random chance. The suspect events are broadly distributed in regions that correlate with historical activity in the Great Basin. The events are not uniquely associated with known volcanic activity, or with zones that were previously active with microearthquakes or aftershock sequences. The magnitudes of the largest triggered events appear to decrease with distance. With time, the number of suspect events decreases at a rate comparable to the rate of decrease of aftershocks of the Landers and Big Bear earthquakes. Three of the most significant triggered events that that occurred were as follows: Mina, 500 km from Landers, M 4, 36 min after Landers; Smith Valley, 590 km from Landers, M 3.4, 56 min after Landers; and Little Skull Mountain, 280 km from Landers, M 5.6, 22.3 hr after Landers. The evidence for triggering is particularly strong in the case of the Little Skull Mountain event, where an increased rate of microseismicity was evident as soon as small events could be identified in the coda of the Landers earthquake. We evaluate the seismic history for the past 3 yr to understand what was unique about the Landers earthquake. This includes identifying the previous earthquakes most likely to have caused the strongest shaking in various frequency bands. Based on a simple screening model, the strains from the Landers earthquake were uniquely large at low frequencies, but at high frequencies they were exceeded frequently by small, more local events. Thus, we hypothesize that the cause of triggering is low-frequency dynamic strains, at periods of about 10 sec or greater, and that there is a regional threshold that must be exceeded, since previous events with calculated strains that were almost as strong were not causes of widespread triggering. This mechanism for triggering satisfies the criterion of being a relatively rare phenomenon, since it is likely to occur only when a large long-period wave is radiated into an area where strain has been building slowly toward the point where faults are unstable.
Debi Kilb - One of the best experts on this subject based on the ideXlab platform.
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a strong correlation between induced peak dynamic coulomb stress change from the 1992 m7 3 landers california earthquake and the hypocenter of the 1999 m7 1 hector mine california earthquake
Journal of Geophysical Research, 2003Co-Authors: Debi KilbAbstract:The 1992 M7.3 Landers earthquake may have played a role in triggering the 1999 M7.1 1 Hector Mine earthquake as suggested by their close spatial (∼20 km) proximity. Current investigations of triggering by static stress changes produce differing conclusions when small variations in parameter values are employed. Here I test the hypothesis that large-amplitude dynamic stress changes, induced by the Landers rupture, acted to promote the Hector Mine earthquake. I use a flat layer reflectivity method to model the Landers earthquake displacement seismograms. By requiring agreement between the model seismograms and data, I can constrain the Landers main shock parameters and velocity model. A similar reflectivity method is used to compute the evolution of stress changes. I find a strong positive correlation between the Hector Mine hypocenter and regions of large (>4 MPa) dynamic Coulomb stress changes (peak Δσ f (t)) induced by the Landers main shock. A positive correlation is also found with large dynamic normal and shear stress changes. Uncertainties in peak Δσ f (t) (1.3 MPa) are only 28% of the median value (4.6 MPa) determined from an extensive set (160) of model parameters. Therefore the correlation with dynamic stresses is robust to a range of Hector Mine main shock parameters, as well as to variations in the friction and Skempton's coefficients used in the calculations. These results imply dynamic stress changes may be an important part of earthquake trigging, such that large-amplitude stress changes alter the properties of an existing fault in a way that promotes fault failure.
Selwyn I Sacks - One of the best experts on this subject based on the ideXlab platform.
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stress triggering of the 1999 hector mine earthquake by transient deformation following the 1992 landers earthquake
Bulletin of the Seismological Society of America, 2002Co-Authors: Fred F Pollitz, Selwyn I SacksAbstract:The M 7.3 June 28, 1992 Landers and M 7.1 October 16, 1999 Hector Mine earthquakes, California, both right lateral strike-slip events on NNW-trending subvertical faults, occurred in close proximity in space and time in a region where recurrence times for surface-rupturing earthquakes are thousands of years. This sug- gests a causal role for the Landers earthquake in triggering the Hector Mine earth- quake. Previous modeling of the static stress change associated with the Landers earthquake shows that the area of peak Hector Mine slip lies where the Coulomb failure stress promoting right-lateral strike-slip failure was high, but the nucleation point of the Hector Mine rupture was neutrally to weakly promoted, depending on the assumed coefficient of friction. Possible explanations that could account for the 7-year delay between the two ruptures include background tectonic stressing, dissi- pation of fluid pressure gradients, rate- and state-dependent friction effects, and post- Landers viscoelastic relaxation of the lower crust and upper mantle. By employing a viscoelastic model calibrated by geodetic data collected during the time period between the Landers and Hector Mine events, we calculate that postseismic relaxa- tion produced a transient increase in Coulomb failure stress of about 0.7 bars on the impending Hector Mine rupture surface. The increase is greatest over the broad surface that includes the 1999 nucleation point and the site of peak slip further north. Since stress changes of magnitude greater than or equal to 0.1 bar are associated with documented causal fault interactions elsewhere, viscoelastic relaxation likely con- tributed to the triggering of the Hector Mine earthquake. This interpretation relies on the assumption that the faults occupying the central Mojave Desert (i.e., both the Landers and Hector Mine rupturing faults) were critically stressed just prior to the Landers earthquake.
Manmohan Parida - One of the best experts on this subject based on the ideXlab platform.
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development of a real time loop mediated isothermal amplification assay for detection of burkholderia mallei
Transboundary and Emerging Diseases, 2018Co-Authors: Apoorva Saxena, Jyoti S. Kumar, A.k. Goel, Sandeep Singh, Manmohan ParidaAbstract:: Burkholderia mallei is the aetiological agent of Glanders, a highly contagious and re-emerging zoonotic disease. Early diagnosis of Glanders is critically important to ensure timely treatment with appropriate antibiotics in humans, and to prevent spread of infection in animals. Molecular detection of B. mallei has always been troublesome because of its genetic similarity with Burkholderia pseudomallei, the causative agent of melioidosis. In present investigation, a set of six B. mallei-specific primers were designed and a simple, rapid, specific and sensitive real-time loop-mediated isothermal amplification (LAMP) assay was developed for detection of B. mallei. The LAMP assay could detect as low as 1 pg of B. mallei genomic DNA and 5.5 × 103 CFU/ml of B. mallei in spiked human blood. The assay was highly specific for B. mallei as it did not cross-react with other bacterial strains used in the study. The established LAMP assay is field adaptable and can be a better and viable alternative to PCR-based techniques for detection of B. mallei in Glanders endemic areas with resource-limited settings.
James R Rice - One of the best experts on this subject based on the ideXlab platform.
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triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake
Journal of Geophysical Research, 2002Co-Authors: Karen R Felzer, Thorsten W Becker, Rachel E Abercrombie, Goran Ekstrom, James R RiceAbstract:[1] There is strong observational evidence that the 1999 MW 7.1 Hector Mine earthquake in the Mojave Desert, California, was triggered by the nearby 1992 MW 7.3 Landers earthquake. Many authors have proposed that the Landers earthquake directly stressed the Hector Mine fault. Our model of the Landers aftershock sequence, however, suggests there is an 85% chance that the Hector Mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the Landers main shock. We perform our model simulations using the Monte Carlo method based on the Gutenberg-Richter relationship, Omori's law, Bath's law, and assumptions that all earthquakes, including aftershocks, are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do. In general, our simulations show that if it has been more than several days since an M ≥ 7 main shock, most new aftershocks will be the result of secondary triggering. These secondary aftershocks are not physically constrained to occur where the original main shock increased stress. This may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static Coulomb stress triggering studies.