Earthquake source nucleation process in the zone of a permanently creeping deep fault

• Published in: Izvestiya. Physics of the solid earth 2008-10, Vol.44 (10), p.839-845
• Main Authors: Lykov, V. I., Mostryukov, A. O.
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Earthquake prediction; Earthquakes; Fault lines; Geophysics; Geophysics/Geodesy; Plate tectonics; Rigidity; Seismic activity; Seismology
• ISSN: 1069-3513; 1555-6506
• DOI: 10.1134/S106935130810011X

The worldwide practice of earthquake prediction, whose beginning relates to the 1970s, shows that spatial manifestations of various precursors under real seismotectonic conditions are very irregular. As noted in [Kurbanov et al., 1980], zones of bending, intersection, and branching of deep faults, where conditions are favorable for increasing tangential tectonic stresses, serve as “natural amplifiers” of precursory effects. The earthquake of September 28, 2004, occurred on the Parkfield segment of the San Andreas deep fault in the area of a local bending of its plane. The fault segment about 60 km long and its vicinities are the oldest prognostic area in California. Results of observations before and after the earthquake were promptly analyzed and published in a special issue of Seismological Research Letters (2005, Vol. 76, no. 1). We have an original method enabling the monitoring of the integral rigidity of seismically active rock massifs. The integral rigidity is determined from the relative numbers of brittle and viscous failure acts during the formation of source ruptures of background earthquakes in a given massif. Fracture mechanisms are diagnosed from the steepness of the first arrival of the direct P wave. Principles underlying our method are described in [Lykov and Mostryukov, 1996, 2001, 2003]. Results of monitoring have been directly displayed at the site of the Laboratory ( http://wwwbrk.adm.yar.ru/russian/1_512/index.html ) since the mid-1990s. It seems that this information has not attracted the attention of American seismologists. This paper assesses the informativeness of the rigidity monitoring at the stage of formation of a strong earthquake source in relation to other methods.