Seismicity of the Incoming Plate at the Mariana Trench Located Using an Ocean Bottom Seismograph Array

Abstract:

We locate earthquakes occurring near the Mariana Trench using an ocean bottom seismograph (OBS) array to study the role of incoming plate seismicity in hydrating the mantle as well as to constrain seismicity at the updip end of the Mariana subduction thrust. The array consisted of 20 broadband OBSs, and 5 temporary broadband seismographs deployed on nearby islands from February 2012 to February 2013. The OBS water depths were limited to 6 km or less, so they were deployed surrounding the trench and 5 hydrophones were deployed in the water column near the trench axis. Preliminary results indicate that seismicity in the incoming plate begins about 120 km west of the trench axis, with the highest seismicity levels found near the trench axis itself. Many of the incoming plate earthquakes locate near large fault scarps identified in seafloor bathymetry. In the forearc, Mariana shallow thrust seismicity begins where the plate interface is at 15-20km depth. There is a strong contrast in velocity structure across the trench, which causes difficulty in determining precise locations and depths. Further work will clarify the depths and focal mechanisms of the recorded earthquakes.