Abstract Title Recent Seismicity and Surface Deformation at Lake Tahoe: An Update on Lower Crustal Magma Movement
Abstract Author William C. Hammond Geoff Blewitt Corne Kreemer Hans-Peter Plag John Anderson Ken Smith
Abstract Text In late 2003 a lower crustal seismic swarm (29-33 km depth) beneath the north end of Lake Tahoe, CA/NV was accompanied by an ~1 cm northeastward motion of the continuous GPS site SLID on Slide Mountain, NV. The position and motion of SLID with respect to the northeast dipping planar cluster of seismicity (green dots in Figure) suggested that the earthquakes and surface motion were caused by a progressive filling of a crack with magma, injected from below [Smith et al., 2004]. This activity began again in mid-2005 when another movement, of size and direction nearly equal to the 2003 event, was observed with GPS at SLID. However, this time the associated cluster of seismic activity was shallower and more energetic. The distribution of shallow seismicity follows a spatial pattern that is strongly focused to the north of the original swarm, and divided into separate northwest, and northeast trending clusters (yellow dots north of Lake Tahoe). This distribution suggests some influence by the tectonic structures of the Great Basin/Sierra Nevada transition zone, and may provide some clues about the state of stress in this active transtensional system.
We will provide an up-to-date GPS position time series for the site SLID, and present new data from our GPS deployments around the location of the swarm and its related surface deformation. We have established 9 new GPS sites around the Tahoe region that can eventually help constrain the depth, location and motion of deep motions of fluids similar to those that have already been observed, and also eventually provide much needed observations to constrain the active crustal kinematics of the westernmost basin of the Basin and Range.
Smith, K.D., D. von Seggern, G. Blewitt, L. Preston, J.G. Anderson, B.P. Wernicke, and J.L. Davis, 2004, Evidence for Deep Magma injection beneath Lake Tahoe, Nevada-California, Science, 305, 1277-1280.