On 21 September 2013 two earthquakes (M 4.8 and 3.0, focal depths >70 km) occurred in the lithospheric mantle beneath central Wyoming, which provide a rare opportunity to investigate the lithosphere rheology and dynamics. We determined a detailed 3-D P wave tomography in the source area of the Wyoming earthquakes using a large number of high-quality traveltime data of local earthquakes and teleseismic events. Our results show that the 2013 Wyoming earthquakes occurred in an isolated high-velocity (high-V) anomaly which extends down to a depth of ~160 km. We propose two possible scenarios about the cause of the 2013 Wyoming earthquakes. One is that the high-V anomaly reflects a remnant of the subducted Farallon slab which fractured under long-term negative buoyancy and heating by the infilling asthenosphere. The other is removing of a dense mantle lithospheric root. The present results shed new light on the rheology and seismotectonics of the continental lithosphere.
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