Seismicity of the Antarctic Great Wall Station area during 2015−2017

The South Shetland Islands are located at the northern part of the Antarctic Peninsula in the West Antarctica. The region is subject to the direct or indirect influences from the Pacific Plate, the Antarctic Plate, the South American Plate, the Scotia Plate and the Phoenix Plate, which has resulted in significant tectonic activities, including subduction, rifting and volcanic magmatism. The global earthquake catalog shows that this region exhibits a higher level of seismicity in comparison to the stable Antarctic continent interior. The extreme climatic conditions of the Antarctic continent present significant challenges to seismic observation, and the level of seismological research conducted on the continent is limited. The distribution of seismic stations in the South Shetland Islands region is relatively sparse, which limits the seismic monitoring capacity of the region and consequently affects our understanding of the seismicity in the region. The Chinese Antarctic Great Wall Seismic Station （CCZ） is located on King George Island in the South Shetland Islands. Following the reconstruction and resumption of observation in 2010, the quality of seismic observation has been remarkably enhanced, thereby considerably improving the monitoring capability of small earthquakes in the Great Wall Station area and providing data support for a comprehensive understanding of the seismicity in the South Shetland Islands region.

We used the single station location method of interlaced grid search to obtain earthquake catalog based on the broadband three-component waveform data recorded at CCZ during 2015−2017. Firstly, the P wave and S wave arrivals of the local seismic events are identified through visual analysis, and the events with clear Pg and Sg waves are selected for amplitude measurements. The arrival time difference, incidence angle and back azimuth of the events can be calculated. The interlaced grid search method initially establishes a set of grids for searching and location, and searching for three elements of arrival time difference, incidence angle, and back azimuth, respectively. Then subsequently spatially translates the grids to obtain the location results of searching different grids. Finally, it evaluates the location results by calculating the standard deviation of the results obtained by the same set of data in the search of different grids. This method effectively overcomes the limitations of single set grid searching and location by a spatial intersection of multiple sets of grids. It has the potential to enhance the spatial sampling rate of earthquake location while simultaneously ensure the reliability and precision of the outcomes through the integration of multiple grid systems in space.

In this study, 1 452 local seismic events were identified, and 112 events with high signal-to-noise ratios were located, of which 87% of the events have an epicentral distance standard deviation and a depth standard deviation smaller than the grid division size of 1.0 km, indicating that the differences of grid models have less influence on the results in the location method of interlaced grid search, and the location results are stable and reliable. In this study, the earthquake catalog of CCZ and the events distribution in South Shetland Islands and its surrounding areas are obtained. During this period, the comparison between the CCZ catalog and the ANSS catalog in terms of magnitude, focal depth, and the number of located events suggests that CCZ effectively improves the seismic monitoring capability of the area, and that the use of direct P wave initial amplitude for calculating the angle of incidence better constrains the focal depth of local seismic events. The distribution of events shows that the events mainly spread along the NE direction in the South Shetland Islands region, with the maximum magnitude of M_L4.8, the minimum magnitude of M_L1.3, and the focal depth ranging from 2 to 134 km. The seismicity in the Antarctic Great Wall Station area is stronger than that of the stable interior of the Antarctic continent. The spreading of the Bransfield Strait was accompanied by extensive volcanism, and this study identifies clusters of earthquakes on Deception Island and its eastern flanks, as well as in the southern part of Greenwich Island, that may be related to the volcanic magmatism caused by subduction. Eleven events with focal depths exceeding 100 km, which have occurred beneath the lithosphere, were detected in the forearc region close to the South Shetland Trench. The locations of these events suggest that the subduction may have occurred in this region, which provides direct seismological evidence that the subduction of the Phoenix Plate is still continuing.