Buried shallow fault slip from the South Napa earthquake revealed by near-field geodesy

作者：Brooks Benjamin A; Minson Sarah E; Glennie Craig L; Nevitt Johanna M; Dawson Tim; Rubin Ron; Ericksen Todd L; Lockner David; Hudnut Kenneth; Langenheim Victoria; Lutz Andrew; Mareschal Maxime; Murray Jessica; Schwartz David; Zaccone Dana

来源：Science Advances, 2017, 3(7): e1700525.

DOI：10.1126/sciadv.1700525

Earthquake-related fault slip in the upper hundreds of meters of Earth's surface has remained largely unstudied because of challenges measuring deformation in the near field of a fault rupture. We analyze centimeter-scale accuracy mobile laser scanning (MLS) data of deformed vine rows within +/- 300 m of the principal surface expression of the M (magnitude) 6.0 2014 South Napa earthquake. Rather than assuming surface displacement equivalence to fault slip, we invert the near-field data with a model that allows for, but does not require, the fault to be buried below the surface. The inversion maps the position on a preexisting fault plane of a slip front that terminates similar to 3 to 25 m below the surface coseismically and within a few hours postseismically. The lack of surface-breaching fault slip is verified by two trenches. We estimate near-surface slip ranging from similar to 0.5 to 1.25 m. Surface displacement can underestimate fault slip by as much as 30%. This implies that similar biases could be present in short-term geologic slip rates used in seismic hazard analyses. Along strike and downdip, we find deficits in slip: The along-strike deficit is erased after similar to 1 month by afterslip. We find no evidence of off-fault deformation and conclude that the downdip shallow slip deficit for this event is likely an artifact. As near-field geodetic data rapidly proliferate and will become commonplace, we suggest that analyses of near-surface fault rupture should also use more sophisticated mechanical models and subsurface geomechanical tests.

• 出版日期2017-7