Abstract Title: Applications of EarthScope Initiatives in crutal imaging and 
LIDAR mapping to determine the 'Pulse of the Earthquake Engine'

Abstract Author(s): Bruhn, Ronald - Schuster, Gerard (Dept. Geology and 
Geophysics, University of Utah)  

Abstract: The Basin and Range Province and its margins are an important natural 
laboratory for studying processes and evolution of intra-plate rifting. The 
province's populated regions and environmentally sensitive industrial and 
military facilities also require evaluation of hazards posed by earthquakes. 
Our research group is currently involved in a several year study of the 'pulse 
of the earthquake engine' to determine recurrence patterns of fault rupturing 
in the eastern Basin and Range at time scales of 100 ka to 1 ma using a 
combination of high resolution geophysics together with drilling and dating of 
Quaternary deposits. This work is motivated by the need to better understand 
temporal patterns of fault rupturing for estimating earthquake hazards, and 
also to better define mechanical models of faulting. Important aspects of the 
research include determining the presence or absence of earthquake temporal 
clustering, and the significance of such temporal behavior for fault mechanics. 
We have recently imaged subsurface colluvial deposits related to long-term 
fautling history at several sites in the eastern Basin and Range, and dated 
fault rupturing events as old as 200+ thousand years. New models of fault 
rupture must consider the temporal relationship of rupture patterns to the rise 
and decay of fluid pressure, and rates of tectonic loading that are partly 
controlled by the rheology of the crust and mantle. These latter properties 
must be partly inherited from the protracted tectonic history of the 
continental crust in the Basin and Range given the close spatial correspondence 
of major fault zone segment boundaries with changes in pre-Neogene structures 
and stratigraphy that extend back into the Paleozoic and Precambrian. Several 
initiatives in the EarthScope program can provide critical new information to 
extend this research. These include applying seismic and electromagnetic 
methods to document pore fluid distribution and pressure in the middle and 
lower crust, and defining the spatial variations in crust and mantle 
composition and structure that control the along-strike segmentation and 
down-dip geometry of large normal faults. Specific measurements should include 
Vp/Vs ratio, seismic velocity aniostropy via shear wave splitting, and 
electrical conductivity, as well as reflection and refraction layering. The 
spatial resolution of these measurements must, where possible, be several km2 
or less to reveal significant differences in physical and mechanical properties 
between fault segments that are several tens of kilometers long, and separated 
across strike by 20 km to 30 km. High-resolution LIDAR topographic surveying is 
also required to reveal subtle but significant geomorphology evidence for 
previously undetected surface faulting and folding of Quaternary deposits above 
'blind' or buried faults. Lastly, GPS supplemented by InSAR measurements of 
spatial and temporal variations in strain and displacement fields will be 
critical for determining contemporary rates of fault loading and the spatial 
distribution of strain.