Fault Interaction in Alaska: Static Coulomb Stress Transfer

Abstract

Between 1938 and 2002, most ofthe known major active fault segments in southern Alaska with estimated recurrence intervals of less than 700 years have ruptured. Static (coseismic) Coulomb stress transfer has been modeled from the nine largest (M ≥ 7.5) of these earthquakes. Stresses transferred from these sources, ranging from less than 0.001 MPa (0.01 bar) to 1 MPa (10 bars) locally, were computed on 30 target fault segments, including 16 segments associated with the above major earthquake sources. Post-1938 cumulative static Coulomb stress transfer in excess of 0.1 MPa preceded failure of the Denali―Totschunda, Sitka, Kodiak, and southern Gulf of Alaska segments. Stress transfer since 1938 indicates the presence of transferred stresses in excess of 0.1 MPa, locally approaching 1 MPa, at seismogenic depths on target fault segments that have not ruptured since 1938, including the Denali Park segments ofthe western Denali fault, the Castle Mountain fault, the Cross Creek fault, the southern part of the Totschunda-Fairweather gap, and the west Yakataga gap. Some segments that have ruptured during or since 1938 have received static Coulomb stress reloading locally in excess of 0.1 MPa. These include the Alaska Peninsula, offshore Fairweather, and northern Queen Charlotte fault segments. Stresses transferred to the slowly slipping Denali-Totschunda fault system can result in significant earthquake probability changes, whereas high slip rates on the Fairweather-Queen Charlotte transform fault system limit the advance toward (or retreat from) time of failure due to transferred stresses.