MAINSHOCK AND AFTERSHOCK ANALYSIS OF THE JUNE 17, 1996, DEEP FLORES SEA EARTHQUAKE SEQUENCE - IMPLICATIONS FOR THE MECHANISM OF DEEP EARTHQUAKES AND THE TECTONICS OF THE BANDA SEA

One of the largest (M-w = 7.8) deep earthquakes (595 km) in recorded h istory occurred beneath the Flores Sea on June 17, 1996. We analyze br oadband body waveforms to determine the seismic source characteristics of this important earthquake. The source time function has a small in itial subevent (5 s duration) followed by three major subevents with a total source duration of 29 s. Directivity analysis indicates an unil ateral rupture to the east-southeast with a subhorizontal rupture leng th of 75 km. A time-independent moment tensor (TIMT) inversion gives a total seismic moment of 5.4 x 10(20) N m (M-w = 7.8). A time-dependen t moment tensor (TDMT) inversion indicates rupture on a near-vertical fault (strike of 130 degrees, dip of 80 degrees SW, rake of -166 degre es) during the first 5 s, releasing 8% of the seismic moment. The majo r part of the moment was released along a shallower dipping plane (str ike of similar to 100 degrees, dip of similar to 55 degrees, rake of s imilar to-45 degrees). This change of faulting geometry may imply that the rupture initiated at a structural, thermal, or phase boundary of high stress concentration and then triggered the major moment release along a regional weak zone. The mainshock produced at least 23 (m(b) > 2.9) aftershocks within the first 3 days. Seventeen of the largest af tershocks were located using the Joint Hypocenter Determination algori thm. The aftershocks define a plane dipping antithetically to the dip of the subducting slab with lateral and depth dimensions of 145 km and 76 km, respectively. The aftershock locations correlate with the sout heast striking nodal plane of the moment tensor mechanism.