HR: 1330h
AN: S12A-0363    [PDF]
TI: The 2002 Denali Fault, Alaska Earthquake Sequence Recorded on the Regional Network: Earthquake Locations, Magnitudes, and Focal Mechanisms
AU: * Ratchkovski, N A
EM: natasha@giseis.alaska.edu
AF: Geophysical Institue, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775-7320 United States
AU: Hansen, R A
EM: roger@giseis.alaska.edu
AF: Geophysical Institue, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775-7320 United States
AB: The largest inland earthquake in North America in almost 150 years struck Alaska on November 3, 2002. It ruptured three different faults ending with a total rupture length of 330 km and maximum vertical and horizontal offsets of 4 m and 8.8 m, respectively. The M 7.9 Denali Fault event was preceded by M 6.7 Nenana Mountain event on October 23, 2002. In response to the magnitude 6.7 and 7.9 events, the Alaska Earthquake Information Center installed a network of temporary instruments for the aftershock monitoring. More than 16,000 aftershocks of both the magnitude 6.7 and 7.9 events have been recorded and located as of the end of December, 2002. The magnitude of completeness of the aftershock catalog varies along the rupture zone. While for the whole catalog the magnitude of completeness is 1.4, it is as low as 1.1 at the western end of the rupture and as high as 2.2 at the eastern end. Estimated b-value for the October-November sequence is 0.7. The aftershocks of the M 6.7 Nenana Mountain event extend 45 km along the Denali Fault pedominately to the west of the epicenter. The 7.9 event had a magnitude 4.4 foreshock which occurred 3.5 hours prior to the mainshock and had right-lateral strike-slip faulting mechanism. The largest aftershock (magnitude 5.8) occurred 20 min after the mainshock, 95 km to the east of the epicenter. Aftershocks of the M 7.9 event present a complex pattern along the rupture zone. In some places, they outline the vertically dipping faults along the main trace of the rupture. However, the cluster centered on the mainshock epicenter occupies a broad region. On its south side, it is outlined closely by the ground rupture along the Susitna Glacier fault, while on the other end it extends over onto the northern side of the Denali fault. In the area east of the Richardson Highway the aftershocks outline dipping structures on both sides of the Denali fault. At the eastern end of the rupture, the aftershocks form a diffuse band extending from the Totcshunda strand towards the main trace of the Denali fault. The majority of the aftershocks are located in the uppper 10 km of the crust. The P-wave first motion focal mechanisms indicate predominantly right-lateral strike-slip and reverse motions. This catalog of focal mechanisms has been used to calculate principal stress directions along the Denali fault trace.
DE: 7215 Earthquake parameters
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting