Regional Earthquakes Recorded by Ocean Bottom Seismometers (OBS) and an Ocean Sub-Bottom Seismometer (OSS IV) on Leg 88

摘要

During Deep Sea Drilling Project (DSDP) Leg 88, an ocean sub-bottom seismometer (OSS IV) was placed in Hole 581C, and an array of ocean bottom seismometers (OBS) was deployed about the hole. Together they provided a 75-day continuous recording of seismic activity. The OBS array, recording for 11 days, detected more than 80 regional and tele-seismic earthquakes, of which only 10 were located by the National Earthquake Information Service (NEIS). The OSS IV, recording for 64 days, provided records of 660 earthquakes of which 59 were located by NEIS. Low frequency mantle P arrivals are observed as first arrivals for events closer than 12 deg; high frequency ocean P (P deg) and ocean S (S deg) arrivals are observed for most intermediate to shallow depth events. A travel time curve based on a sample of 33 earthquakes from 6 to 20 deg agrees well with previous observations for earthquakes with epicentral distances from 12 to 28 deg recorded in the ocean. A comparison of the original, NEIS-located earthquakes recorded on an OBS with those recorded on OSS IV suggests that the borehole seismometer is somewhat more sensitive for earthquake detection than ocean-bottom instruments. This chapter presents a preliminary examination of these excellent data.