The Ulakhan fault surface rupture and the seismicity of the Okhotsk–North America plate boundary

Hindle, David; Sedov, Boris; Lindauer, Susanne; Mackey, Kevin

New field work, combined with analysis of high-resolution aerial photographs, digital elevation models, and satellite imagery, has identified an active fault that is traceable for inline-formula∼90 km across the Seymchan Basin and is part of the Ulakhan fault system, which is believed to form the Okhotsk–North America plate boundary. Age dating of alluvial fan sediments in a channel system that is disturbed by fault activity suggests the current scarp is a result of a series of large earthquakes (inline-formula≥Mw 7.5) that have occurred since inline-formula11.6±2.7 ka. A possible channel feature offset by inline-formula62±4 m associated with these sediments yields a slip rate of inline-formula5.3±1.3 mm yrinline-formula−1, in broad agreement with rates suggested from global plate tectonics. Our results clearly identify the Ulakhan fault as the Okhotsk–North America plate boundary and show that tectonic strain release is strongly concentrated on the boundaries of Okhotsk. In light of our results, the likelihood of recurrence of inline-formulaMw 7.5 earthquakes is high, suggesting a previously underestimated seismic hazard across the region.

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Hindle, David / Sedov, Boris / Lindauer, Susanne / et al: The Ulakhan fault surface rupture and the seismicity of the Okhotsk–North America plate boundary. 2019. Copernicus Publications.

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