A simple method for estimating the horizontal velocity field in wide zones of active deformation-II. Examples from New Zealand, Central Asia and Chile

Abstract

SUMMARY Lamb (1994) has described a simple method for estimating the horizontal velocity field in a wide zone of active deformation. This method is now used to investigate the horizontal velocity or displacement field in part of the New Zealand plate‐boundary zone, Central Asia and southern central Chile. In each region, a range of weighted least‐squares solutions have been found, depending on assumptions about aspects of the internal deformation. In the New Zealand example, observed tectonic rotations are successfully predicted. Solutions for Central Asia place constraints on the manner in which the northward convergence of India into Eurasia is accommodated. Horizontal surface displacement fields are determined for the elastic rebound during the 1960 Chilean great earthquake, based on available retriangulation data and assumptions about the slip vector on the fault. These solutions suggest, but do not prove, a nearly pure thrust event for this earthquake.

Fault slip rates and interseismic deformation in the western Transverse Ranges, California

“…[26] We estimate a regional vertical axis rotation rate of 2.3 ± 0.1°/Myr in a clockwise direction, which is in agreement with the direction of rotation inferred from several past studies but generally slightly slower than most estimates of rotation throughout the western Transverse Ranges [e.g., Donnellan et al, 1993b;Jackson and Molnar, 1990;Lamb, 1994;Luyendyk, 1991;Luyendyk et al, 1980]. For example, using kinematic models of rotation, Lamb [1994]…”

“…Given that the GPS‐model residuals are often large at GPS sites far from station CIRX and many residuals appear to be approximately consistent with rotations about station CIRX, we investigate whether regional variations in rotation rates can at least partially explain the model misfit at the distal GPS sites. Because our main purpose here is to determine fault slip rates and to match the patterns of contraction, a detailed discussion of the potential geologic sources of rotation is beyond the scope of this work; however, we note that unlike strains, which are independent of reference frame, rotations are dependent on reference frame [e.g., Lamb , ].…”

“…We estimate a regional vertical axis rotation rate of 2.3 ± 0.1°/Myr in a clockwise direction, which is in agreement with the direction of rotation inferred from several past studies but generally slightly slower than most estimates of rotation throughout the western Transverse Ranges [e.g., Donnellan et al ., ; Jackson and Molnar , ; Lamb , ; Luyendyk , ; Luyendyk et al ., ]. For example, using kinematic models of rotation, Lamb [] estimates 2.4–3.5°/Myr of clockwise rotation, although the rates are predicted to be rather temporally variable. Using very long baseline interferometry data, Jackson and Molnar [] estimate 3–9°/Myr, and Donnellan et al .…”

Geodetic evidence for a low slip rate in the Altyn Tagh fault system

“…In kinematic views of the Indo-Asian plate collision, India's northward motion is absorbed by slip on a small number of active faults bounding major structural units in the collision zone 4,9,10 . The blocks of continental crust between these major faults are usually modelled as elastic; they deform only in the sense that slip on smaller faults within them may permit slow thickening, or other relatively minor, inelastic changes of shape of each block 9,11,12 .…”

“…The blocks of continental crust between these major faults are usually modelled as elastic; they deform only in the sense that slip on smaller faults within them may permit slow thickening, or other relatively minor, inelastic changes of shape of each block 9,11,12 . In contrast, dynamic models of Asian deformation (models that recognize collisional forces and inferred viscous and elastic properties of the blocks) anticipate deformation throughout the crust and upper mantle 13,14 .…”