Geoinformatika 2017; 2(62) : 14-23 (in Ukrainian)

MODELS OF SEISMIC SOURCES

D. Malytskyy, A. Pavlova, O. Grytsai, O. Astashkina, O.O. Obidina, М.Р. Makhnitskyy, E. Kozlovskyy

Carpathian Branch of the Institute of Geophysics, NAS of Ukraine, 3B, Naukova Str., Lviv, 79060, Ukraine, e-mail: dmytro@cb-igph.lviv.ua, grycaj.oksana@gmail.com, susyinet@gmail.com, sac1@ukr.net, obidinaeriol@gmail.com

Purpose. The paper proposes new methods to determine the parameters of the point and the extended sources of earthquakes.

Design/methodology/approach. The source mechanism of an earthquake is determined by a graphic method from polarities of the P-waves first arrival, emergence angles (or angles of incidence) of the first P-waves at the stations, and station azimuths. The accuracy of the nodal planes on the focal sphere in the graphic method is significantly improved by accounting for important additional information contained in fuzzy P-wave arrivals and the logarithm of S- to P-wave amplitude ratio. Emergence angles of P-waves at the stations, and station azimuths are calculated using a software package for each of the events. In case of an insufficient number of stations, we propose an earthquake mechanism to determine by inversion only waveforms of direct P-waves at the stations.

Findings. The inversion method consists in determining seismic moment tensor at a station and subsequently trans­lating the solution into the event’s hypocenter. The extended source is modeled by solving the inverse problem as a set of point sources and their parameters. The problem of the earthquake source is therefore solved in two steps: 1) identification of source mechanism; 2) determination of slip, rise time, and rupture time for each of the elementary point sources. Correctness of the problem is improved by adding a constraint on the horizontal component of wave number.

Practical value /implications. Using the data from the project SIV, we present practical application of the methods to determine both the point and the extended sources.

Keywords: point source, distributed source rise time, rupture time, moment tensor, fault plane, graphic method.

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