HR: 1340h
AN: S53B-1094    [Abstracts]
TI: Possible Biases in Characteristic Earthquake and Seismic Hazard Studies: Illustrations for the Wasatch, New Madrid, North Africa, and Eastern Canadian Seismic Zones
AU: * Swafford, L
EM: swafford@earth.northwestern.edu
AF: University of Northwestern, Department of Geology, Evanston, IL 60208 United States
AU: Stein, S
EM: seth@earth.northwestern.edu
AF: University of Northwestern, Department of Geology, Evanston, IL 60208 United States
AU: Newman, A
EM: anewman@lanl.gov
AF: Los Alamos National Laboratory, EES-9 MS D462, Los Alamos, NM 87545 United States
AU: Friedrich, A
EM: anke@gps.caltech.edu
AF: Universität Hannover, Institute für Geologie und Paläontologie, Hannover, 30167 Germany
AB: Attempts to study earthquake recurrence in space and time are limited in simple but frustrating ways by the short history of instrumental seismology compared to the long and variable recurrence time of large earthquakes. If major seismicity is spread uniformly with a seismic zone but the recurrence interval is long compared to the earthquake record, apparent differences in seismic hazard within the seismic zone inferred from the earthquake history are likely to simply reflect the short earthquake record. Simple numerical simulations suggest that this may be the case for the concentrated areas of high predicted hazard with seismic zones in North Africa, along the St. Lawrence valley, and the eastern coast of Canada. If so, with more time and a longer earthquake record, large earthquakes would likely occur over the entire seismic zone and show that the real hazard is uniform. Similarly, large earthquakes are likely to appear "characteristic", more frequent than would be inferred from the rates of smaller ones, for two reasons. First, a short history is likely to overestimate the rate of large earthquakes because fractions of earthquakes cannot be observed. Second, because the rates of small earthquakes are typically determined from the seismological record whereas the rates of large earthquakes are inferred from paleoseismology, biases in estimating paleomagnitudes can produce apparent characteristic earthquakes, as appears to have occurred for New Madrid. A further complexity is illustrated by results for the Wasatch seismic zone, where some studies find characteristic earthquake behavior whereas others do not. The discrepancy arises primarily because some studies consider the entire Wasatch front area whereas others focus on the Wasatch fault, on which only some of the smaller earthquakes but all of the large paleoearthquakes occur. Similar situations may arise in other seismic zones containing a major fault and a number of smaller ones.
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005