The Role of Active-Source Seismology in EarthScope Gary Fuis U.S. Geological Survey

Trans-Canada Crustal Cross-Section

50 km Cook et al., 2001

Flat Moho beneath crustal ramp Monashee Complex Central Southern Cordillera

COCORP

Trans-Canada Crustal Cross-Section

Active-Source Seismic Methods

Active-source seismology falls into 2 broad, overlapping categories: Refraction seismology --gives a fuzzy image of structure but provides constraints on rock composition Reflection seismology --gives a detailed image of structure but provides little constraint on rock composition

Two Methods for Analyzing Refraction and Reflection Data Inverse modeling (tomography) Forward modeling

Refraction seismology Inverse modeling (tomography)

Refraction seismology Forward modeling

Reflection seismology

Reflections should be here

Conclusions 1. The crust is an important layer to image- -perhaps the most important for understanding Earth processes present and past. Currently, Earthscope has no definite plans or money to image the crust in a systematic way. 2. Reflection profiling is the chief tool for observing the crust. 3. We need, however, multidisciplinary data collection, using all the methods of investigation included in Complementary Geophysics, to obtain the best constrained understanding of lithosphere. 4. LITHOPROBE provides a good model for how to proceed. (Ron Clowes did not pay me to say this.) 5. Our COCORP "transects" of the 1970's and 1980's need to be replaced with at least one transect across the U.S. from margin to margin, taking advantage of the tremendous improvements in hardware and software/processing since those days in order to produce modern images like the Canadians have done.

Conclusions 3. We need, however, multidisciplinary data collection, using all the methods of investigation included in Complementary Geophysics, to obtain the best constrained understanding of lithosphere. 4. LITHOPROBE provides a good model for how to proceed. (Ron Clowes did not pay me to say this.) 5. Our COCORP "transects" of the 1970's and 1980's need to be replaced with at least one transect across the U.S. from margin to margin, taking advantage of the tremendous improvements in hardware and software/processing since those days in order to produce modern images like the Canadians have done.

Conclusions 5. Our COCORP "transects" of the 1970's and 1980's need to be replaced with at least one transect across the U.S. from margin to margin, taking advantage of the tremendous improvements in hardware and software/processing since those days in order to produce modern images like the Canadians have done.