New constraints on tectonics of interior Alaska: Earthquake locations, source mechanisms, and stress regime

We used the joint hypocenter determination (JHD) method to relocate 3611 crustal earthquakes that occurred from 1988 to 1999 in central Alaska. The new earthquake locations provide more details on the structure of the Kantishna cluster and better locations for the aftershock sequence of the 29 November 2000 M-L 5.6 earthquake in the Minto Flats seismic zone. The JHD locations for the aftershocks of the 1995 M-W 6.0 Minto Flats earthquake and 22 October 1996 M-W 5.8 earthquake near the Denali fault are also available. A catalog, of 196 fault-plane solutions consisting of the moment tensor solutions for the earthquakes with magnitude 4.0 or above and P-wave first-motion solutions for the earthquakes with magnitude 3.4 and above that occurred from 1988 to 2000 was composed. Moment tensor solutions were calculated using regional broadband data. This catalog was used to calculate principal stress orientations in the crust. The stress orientations change across central Alaska. In particular, the maximum principal stress orientation rotates clockwise from SE-NW to SSW-NNE direction as one moves from west to east. These stress orientations are consistent with the stress field transferred from the plate convergence in southern Alaska. In addition, we tested different velocity structures in the moment tensor inversion procedure to identify velocity models for calculating the Green's functions. The moment tensor inversion study shows that it is possible to obtain a reliable moment tensor solution for moderate-sized earthquakes (M-L greater than or equal to 4) using three-component records from a single broadband station when the epicentral distances are between 50 and 300 km.