Seismic Anisotropy Map of Western U.S.

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Figure 1. Shear wave splitting results from 26 stations plotted on western U.S. elevation map. Bars by station names denote mean fast direction from the best measurements; length of bars is proportional to delay times as in the lower left of the figure. Red bars indicate fast direction in the upper layer where resolved from the waveform data. Dashed bars are used to indicate unconstrained measurements based on 3 or fewer records. Note (Table 3) that two-later solutions for stations PFO and SVD above the souhern San Andreas fault are not strongly preffered over a single-layer. At station ORV, a cross sign is used to indicate absence of splitting. Approximate present boundary of the Gorda plate is shown from Jachens and Griscom (1983) and Severinghaus and Atwater (1989). Queries indicate regions where knowledge of the boundaries is poor. Central Walker Lane Belt (WLB) (Hardyman and Oldow, 1991), main trace of the San Andreas and Garlock Faults (GF) are also shown. Absolute plate motion (APM) direction for the North American Plate (Gripp and Gordon, 1990), Pacific and North American relative plate motion are indicated by thick black arrows.

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