Overlooked earthquakes on and around the Antarctica plate: identification and location of 1999 shallow depth events

Abstract

As a contribution to the study of high-latitude seismicity on the Antarctica plate, we have developed a procedure to identify and locate previously unnoticed earthquakes by using broadband records of 29 stations operating in the Southern Hemisphere. A first approach of the method consists of visually examining continuous records from GEOSCOPE and GSN stations for Rayleigh-waves associated with earthquakes missing in the NEIC monthly catalogue. Two hundred ten earthquakes were identified that had no corresponding locations in the 1999 NEIC catalogue. Among them, 88 events, with magnitude ranging from 3.7 to 5.2, and identified on at least four stations, have been located by using an epicenter location algorithm based on regional Rayleigh-wave propagation models. The precision of the location, depending both on the selected propagation model and the phase picking accuracy, is around 100 km. Most of the reported earthquakes occurred on the plate boundaries, principally along the South-Indian and Pacific ridges. A few epicenters have been located inside the Antarctica plate, far from the plate limits. Among them, only two earthquakes occurring on the continent itself are reported. About half of the events located in our study are reported by the PIDC (Prototype International Data Center). Three earthquakes, with magnitudes ranging from 4.7 to 5.2, reported neither by NEIC nor by PIDC, are sufficiently energetic to be recorded in most broad-band stations operating around the world. Considerations concerning the local crustal structure and the physical processes at the source are involved in interpreting these observations.