CAN THE SEISMO-LINEAMENT ANALYSIS METHOD [SLAM] FIND THE SURFACE TRACE OF FAULTS KNOWN TO HAVE RUPTURED DURING LARGE [AND SMALL] EARTHQUAKES?

The Seismo-Lineament Analysis Method (SLAM) has been developed to locate faults that are probably seismogenic. SLAM may be particularly useful in identifying seismogenic faults in areas where the fault does not cross datable Holocene material at the ground surface. The fault-plane solution is projected from the boundaries of the uncertainty region around the earthquake focus to the surface of a DEM to define a "seismo-lineament" -- a zone within which the surface trace of the fault associated with the earthquake is likely to be located. Fieldwork is then undertaken to determine whether the seismo-lineament contains a fault with an orientation and slip direction that is compatible with the fault-plane solution.

Are seismogenic faults sufficiently planar for SLAM to be useful? We evaluated this question by gathering data from 6 earthquakes with known surface rupture, including the Parkfield (2004, M6), Denali (2002, M7.9), Hector Mine (1999, M7.1), Superstition Hills (1987, M6.2 and M6.6), and Borah Peak (1983, M7.3) earthquakes. In these cases, the ground-rupture zone associated with the main shock was located within the seismo-lineament.

Can small earthquakes be used to find faults capable of producing large earthquakes? Small earthquakes result from slip on small fault patches, which are commonly located along established faults that have produced large earthquakes. That is, small earthquakes are not necessarily associated with small isolated faults. When a fault-plane solution from a small earthquake correlates spatially with a long, brittle-cataclastic fault exposed at the ground surface, it may be a distant aftershock of a large prehistoric earthquake. SLAM was applied using focal data from aftershocks of several well-recorded major earthquakes. Result: the fault rupture zone associated with the main shock was located within the seismo-lineament in each case. Small earthquakes can be used to find the faults associated with much larger earthquakes.