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U.S. Geological Survey
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- PublicationOpen AccessVariability in synthetic earthquake ground motions caused by source variability and errors in wave propagation models(2019-06-24)
; ; ; ; ;; ; Numerical simulations of earthquake ground motions are used both to anticipate the effects of hypothetical earthquakes by forward simulation and to infer the behaviour of the real earthquake source ruptures by the inversion of recorded ground motions. In either application it is necessary to assume some Earth structure that is necessarily inaccurate and to use a computational method that is also inaccurate for simulating the wavefield Green's functions. We refer to these two sources of error as ‘propagation inaccuracies’, which might be considered to be epistemic. We show that the variance of the Fourier spectrum of the synthetic earthquake seismograms caused by propagation inaccuracies is related to the spatial covariance on the rupture surface of errors in the computed Green's functions, which we estimate for the case of the 2009 L'Aquila, Italy, earthquake by comparing erroneous computed Green's functions with observed L'Aquila aftershock seismograms (empirical Green's functions). We further show that the variance of the synthetic seismograms caused by the rupture variability (aleatory uncertainty) is related to the spatial covariance on the rupture surface of aleatory variations in the rupture model, and we investigate the effect of correlated variations in Green's function errors and variations in rupture models. Thus, we completely characterize the variability of synthetic earthquake seismograms induced by errors in propagation and variability in the rupture behaviour. We calculate the spectra of the variance of the ground motions of the L'Aquila main shock caused by propagation inaccuracies for two specific broad-band stations, the AQU and the FIAM stations. These variances are distressingly large, being comparable or in some cases exceeding the data amplitudes, suggesting that the best-fitting L'Aquila rupture model significantly overfits the data and might be seriously in error. If these computed variances are typical, the accuracy of many other rupture models for past earthquakes may need to be reconsidered. The results of this work might be useful in seismic hazard estimation because the variability of the computed ground motion, caused both by propagation inaccuracies and variations in the rupture model, can be computed directly, not requiring laborious consideration of multiple Earth structures.283 28 - PublicationRestrictedSurface Rupture and Slip Distribution of the Denali and Totschunda Faults(2004-12)
; ; ; ; ; ; ; ; ; ; ; ;Haeussler, P. J.; U.S. Geological Survey ;Schwartz, D. P.; U.S. Geological Survey ;Dawson, T. E.; U.S. Geological Survey ;Stenner, H. D.; U.S. Geological Survey ;Lienkaemper, J. J.; U.S. Geological Survey ;Sherrod, B.; U.S. Geological Survey ;Cinti, F. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Montone, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Craw, P. A.; U.S. Geological Survey ;Crone, A. J.; State of Alaska, Department of Natural Resources, Fairbanks, Alaska ;Personius, S. F.; U.S. Geological Survey; ; ; ; ; ; ; ; ; ; The 3 November 2002 Denali fault, Alaska, earthquake resulted in 341 km of surface rupture on the Susitna Glacier, Denali, and Totschunda faults. The rupture proceeded from west to east and began with a 48-km-long break on the previously unknown Susitna Glacier thrust fault. Slip on this thrust averaged about 4 m (Crone et al., 2004). Next came the principal surface break, along 226 km of the Denali fault, with average right-lateral offsets of 4.5–5.1 m and a maximum offset of 8.8 m near its eastern end. The Denali fault trace is commonly left stepping and north side up. About 99 km of the fault ruptured through glacier ice, where the trace orientation was commonly influenced by local ice fabric. Finally, slip transferred southeastward onto the Totschunda fault and continued for another 66 km where dextral offsets average 1.6–1.8 m. The transition from the Denali fault to the Totschunda fault occurs over a complex 25-km-long transfer zone of right-slip and normal fault traces. Three methods of calculating average surface slip all yield a moment magnitude of Mw 7.8, in very good agreement with the seismologically determined magnitude of M 7.9. A comparison of strong-motion inversions for moment release with our slip distribution shows they have a similar pattern. The locations of the two largest pulses of moment release correlate with the locations of increasing steps in the average values of observed slip. This suggests that slipdistribution data can be used to infer moment release along other active fault traces.141 26 - PublicationOpen AccessSurface Rupture of the November 2002 M7.9 Denali Fault Earthquake, Alaska, and Comparison to Other Strike-Slip Ruptures(2004-08)
; ; ; ; ; ; ; ; ; ;Haeussler, P. J.; U.S. Geological Survey, Anchorage, AK ;Schwartz, D. P.; U.S. Geological Survey, Menlo Park, CA ;Dawson, T. E.; U.S. Geological Survey, Menlo Park, CA ;Stenner, H. D.; U.S. Geological Survey, Menlo Park, CA ;Lienkaemper, J. J.; U.S. Geological Survey, Menlo Park, CA ;Cinti, F. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Montone, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Sherrod, B.; U.S. Geological Survey, Seattle, WA ;Craw, P.; Division of Geological and Geophysical Surveys, Fairbanks, AK; ; ; ; ; ; ; ; On November 3, 2002, a moment-magnitude (Mw) 7.9 earthquake produced 340 km of surface rupture on the Denali fault and two related faults in central Alaska. The rupture, which proceeded from west to east, began with a 40-km-long break on a previously unknown thrust fault. Estimates of surface slip on this thrust were 3-6 m. Next came the principal surface break, along 220 km of the Denali fault. There, right-lateral offset averaged almost 5 m and increased eastward to a maximum of nearly 9 m. Finally, slip turned southeastward onto the Totschunda fault, where dextral offsets up to 3 m continued for another 70 km. This three-part rupture ranks among the longest documented strike-slip events of the past two centuries. The surface-slip distribution supports and clarifies models of seismological and geodetic data that indicated initial thrusting followed by rightlateral strike slip, with the largest moment release near the east end of the Denali fault. The Denali fault ruptured beneath the Trans-Alaska oil pipeline. The pipeline withstood almost 6 m of lateral offset, because engineers designed it to survive such offsets based on pre-construction geological studies. The Denali fault earthquake was typical of large-magnitude earthquakes on major intracontinental strike-slip faults, in the length of the rupture, the multiple fault strands that ruptured, and the variable slip along strike.156 559 - PublicationOpen Access
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