The deep structure of the Olyutorskii earthquake rupture zone in the Koryak Upland: Geophysical evidence

Abstract

This paper considers the data of magnetotelluric sounding (MTS) and gravity and magnetic sur veys, as well as other geological information. We describe the methods that were used in making the observa tions and for interpretation of MTS data. We focus on incorporating the influence of the shift effect and the coast effect. Generalized geoelectric sections are based on mean longitudinal curves, which are less subject to distortion. Transverse curves were used for fault identification. The geoelectric sections include a sedimen tary volcanogenic layer, a high ohmic crust, and a conductive lithosphere layer. They contain faults that were detected from the divergences between oriented MTS curves and other data. The deep seated faults in the Vyvenka basin have surface expression in the form of seismotectonic discontinuities that extend for 80 and 140 km. It was found that the hypocenters of the Olyutorskii earthquake and its aftershocks were in the crustal layer above the conductive lithosphere layer. Most aftershock hypocenters are typically situated in the area of the deep fault. We discuss a possible origin of the conductive lithosphere layer and of deep faults.

Enigma of the Olyutorskii Earthquake Resolved by SAR Interferometry

“…The depths of these earthquakes do not exceed 27 km, with an uncertainty better than 5 km for 78% of them (Lander, Levina, Ivanova, 2010). Therefore, they were located within the crust, which is estimated to be 40 km thick (Moroz, Moroz, Loginov, 2015). Although there is a large uncertainty in the depth estimate, the averaged aftershock depth consistently increases from <5 km in the NW part of the aftershock's cloud to 20-25 km in its SW part.…”

“…2 by orange lines I and II. The Vyvenskii-Vetveiskii zone marks a transition between rocks of varying geological ages and compositions (Fedotov et al, 2011), and it is clearly underlined by gravity and magnetic anomalies (Moroz, Moroz, Loginov, 2015). The northern (Vyvenskii-Vetveiskii) suture dips southeastward, while the southern (Vetlovskii) one dips northwestward (Shapiro, Sololv'ev, 2009).…”

“…Based on geological and geophysical data, a crustal cross-section indicates the presence of several SE dipping crustal boundaries that continue down to the Moho discontinuity in the region where the Vyvenskii -Vetveiskii suture is exposed (Moroz, Moroz, Loginov, 2015). In addition, on vertical sections that run NW-SE across the epicenter area, aftershocks cluster along southeastwards dipping lines (Lander, Levina, Ivanova, 2010).…”