Introduction to the special issue on the 2008 Wenchuan, China, earthquake
[No abstract available]
Bulletin of the Seismological Society of America↗
Geology topics
Z.-K. Shen
Publications and source records attributed to Z.-K. Shen.
Slip maxima at fault junctions and rupturing of barriers during the 2008 Wenchuan earthquake
The disastrous 12 May 2008 Wenchuan earthquake in China took the local population as well as scientists by surprise. Although the Longmen Shan fault zonewhich includes the fault segments along which this earthquake nucleatedwas well known, geologic and geodetic data indicate relatively low (<3 mm yr -1 ) deformation rates. Here we invert Global Positioning System and Interferometric Synthetic Aperture Radar data to infer fault geometry and slip distribution associated with the earthquake. Our analysis shows that the geometry of the fault changes along its length: in the southwest, the fault plane dips moderately to the northwest but becomes nearly vertical in the northeast. Associated with this is a change in the motion along the fault from predominantly thrusting to strike-slip. Peak slip along the fault occurs at the intersections of fault segments located near the towns of Yingxiu, Beichuan and Nanba, where fatalities and damage were concentrated. We suggest that these locations represent barriers that failed in a single event, enabling the rupture to cascade through several fault segments and cause a major moment magnitude (M w ) 7.9 earthquake. Using coseismic slip distribution and geodetic and geological slip rates, we estimate that the failure of barriers and rupture along multiple segments takes place approximately once in 4,000 years. ?? 2009 Macmillan Publishers Limited. All rights reserved.
Nature Geoscience↗
Initiation of deformation of the Eastern California Shear Zone: Constraints from Garlock fault geometry and GPS observations
We suggest a 2-stage deformation model for the Eastern California Shear Zone (ECSZ) to explain the geometry of the Garlock fault trace. We assume the Garlock fault was originally straight and then was gradually curved by right-lateral shear deformation across the ECSZ. In our 2-stage deformation model, the first stage involves uniform shear deformation across the eastern part of the shear zone, and the second stage involves uniform shear deformation across the entire shear zone. In addition to the current shape of the Garlock fault, our model incorporates constraints on contemporary deformation rates provided by GPS observations. We find that the best fitting age for initiation of shear in eastern part of the ECSZ is about 5.0 ?? 0.4 Ma, and that deformation of the western part started about 1.6 Myr later.
Geophysical Research Letters↗
Crustal velocity field near the big bend of California's San Andreas fault
We use geodetic data spanning the 1920–1992 interval to estimate the horizontal velocity field near the big bend segment of California's San Andreas fault (SAF). More specifically, we estimate a horizontal velocity vector for each node of a two-dimensional grid that has a 15-min-by-15-min mesh and that extends between latitudes 34.0°N and 36.0°N and longitudes 117.5°W and 120.5°W. For this estimation process, we apply bilinear interpolation to transfer crustal deformation information from geodetic sites to the grid nodes. The data include over a half century of triangulation measurements, over two decades of repeated electronic distance measurements, a decade of repeated very long baseline interferometry measurements, and several years of Global Positioning System measurements. Magnitudes for our estimated velocity vectors have formal standard errors ranging from 0.7 to 6.8 mm/yr. Our derived velocity field shows that (1) relative motion associated with the SAF exceeds 30 mm/yr and is distributed on the Earth's surface across a band (>100 km wide) that is roughly centered on this fault; (2) when velocities are expressed relative to a fixed North America plate, the motion within our primary study region has a mean orientation of N44°W ± 2° and the surface trace of the SAF is congruent in shape to nearby contours of constant speed yet this trace is oriented between 5° and 10° counterclockwise relative to these contours; and (3) large strain rates (shear rates > 150 nrad/yr and/or areal dilatation rates < −150 nstr/yr) exist near the Garlock fault, near the White Wolf fault, and in the Ventura basin.
Journal of Geophysical Research B: Solid Earth↗