abstract

An accelerogram obtained at Blue Mt. Lake, New York is remarkable for the simplicity of its S-wave pulse. This results from (1) a nearly complete absence of scattering and reflections as second arrivals on the accelerogram, and (2) a very elementary earthquake source. The earthquake identified with this accelerogram had a magnitude mb = 2.2 and a hypocentral distance of about 1 km from the accelerometer. Spectral analysis of the S wave indicates the earthquake had a moment of 8 × 1018 dyne-cm, and a source radius of 20 to 40 m. When the accelerogram is integrated to obtain displacement, there is a step offset of about 5μ associated with a near-field component of the S-wave pulse. The S-wave, including the step offset, can be matched in remarkable detail by a dislocation model with a moment of 8.4 × 1018 dyne-cm.

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