3D geometry of the strain-field at transform plate boundaries: Implications for seismic rupture

Journal Article · Tue Nov 01 04:00:00 EST 1994 · Geophysical Research Letters

DOI:https://doi.org/10.1029/94GL02279· OSTI ID:79482

Bodin, P; Bilham, R ^[1]

---

1. Univ. of Memphis, Memphis, TN (United States)

We examine the amplitude and distribution of slip on vertical frictionless faults in the zone of concentrated shear strain that is characteristic of transform plate boundaries. We study both a 2D and a 3D approximation to this strain field. Mean displacements on ruptures within the zone of concentrated shear strain are proportional to the shear strain at failure when they are short, and are limited by plate displacements since the last major earthquake when they are long. The transition between these two behaviors occurs when the length of the dislocation approaches twice the thickness of the seismogenic crust, approximately the breadth of the zone of concentrated shear strain observed geodetically at transform plate boundaries. This result explains the observed non-linear scaling relation between seismic moment and rupture length. A geometrical consequence of the 3D model, in which the strain-field tapers downward, is that moderate earthquakes with rupture lengths similar to the thickness of the crust tend to slip more at depth than near the surface. Seismic moments estimated from surface slip in moderate earthquakes (M less than or equal to 7) will thus be underestimated. Shallow creep, if its along-strike dimension is extensive, can reduce a surface slip deficit that would otherwise develop on faults on which M less than 7 events are typical. In the absence of surface creep or other forms of off-fault deformation great earthquakes may be necessary features of transform boundaries with downward-tapering strain-fields.

• OSTI ID: 79482
• Journal Information: Geophysical Research Letters, Journal Name: Geophysical Research Letters Journal Issue: 23 Vol. 21; ISSN GPRLAJ; ISSN 0094-8276
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
DEFORMATION
EARTH CRUST
EARTHQUAKES
GEOLOGIC FAULTS
MATHEMATICAL MODELS
PLATE TECTONICS
SHEAR PROPERTIES
SPATIAL DISTRIBUTION