Seismic instruments: article

New data on aftershocks of the December 7, 1988 Spitak Earthquake
I. Gabsatarova1
S. Baranov2
1 Federal Research Center of the Unified Geophysical Survey of RAS, Obninsk, Russia
2 Kola Branch of Federal Research Center of the Unified Geophysical Survey of RAS, Apatity, Russia
Journal: Seismic instruments
Tome: 53
Number: 2
Year: 2017
Pages: 37-57
UDK: 550.
DOI: 10.21455/si2017.2-3
Keywords: aftershock catalogue, strong earthquake, Spitak, seismic stations, double difference algorithm
Аnnotation: The paper is devoted to collecting new data on aftershocks of the Spitak Earthquake occurred on December 7, 1988, Mw =6.8 for the first 20 days after the mainshock. According to the analysis, this part of available data is the least reliable in completeness of information, representativeness, accuracy in determining hypocenters, and, especially, energy classes and magnitudes. The objectives of the study are to collect new data on the aftershocks of the Spitak earthquake for the first 20 days after the mainshock and to determine the parameters of their hypocenters and magnitudes. The collection of new data is performed by analyzing the waveforms and bulletins obtained by seismic stations of regional and global networks. The determination of the hypocenters’ parameters was carried out by minimizing the travel-time residuals with further refinement using double differences algorithm. Digital recordings by the stations of “Obninsk” and “Arti” (D=15-18°) and five more remote stations (D=34-53°) were used to refine the surface wave magnitude of the mainshock and the strongest aftershock. As a result of the research, the aftershock catalog has been significantly improved. It includes already existed materials [ Arefiev et al., 1991] which are refined by the double differences algorithm, as well as the new data obtained by processing bulletins of Caucasian stations. The completeness magnitude of the new catalog Mc =1.9 is the same for first 20 days after the mainshock before the epicentral observations and for the period between 7.12.1988 and 1.12.1989. The new catalog contains information on 2090 aftershocks with magnitudes higher or equal Mc =1.9 for 7.12.1988-31.12.1989. The application of the double differences algorithm in conditions of Caucasus allowed us reliably estimate the error of earthquake epicenter determination in the cluster set: for longitude, the errors do not exceed 4.6 km, latitude - 4 km, and depth - 5 km. The spatial distribution of the aftershock hypocenters of the new catalog corresponds better to the tectonic elements compared to the old data. The new catalog can be used for assessing seismic hazard in the region after strong earthquakes.