Repeated Earthquakes in the Vrancea Subcrustal Source and Source Scaling

Abstract

Abstract. The Vrancea seismic nest, located at the South-Eastern Carpathians Arc bend, in Romania, is a well-confined cluster of seismicity at intermediate depth (60 -180 km). During the last 100 years four major shocks were recorded in the lithosphere body descending almost vertically beneath the Vrancea region: 10 November 1940 (M w 7.7, depth 150 km), 4 March 1977 (M w 7.4, depth 94 km), 30 August 1986 (M w 7.1, depth 131 km) and a double shock on 30 and 31 May 1990 (M w 6.9, depth 91 km and M w 6.4, depth 87 km, respectively). The probability of repeated earthquakes in the Vrancea seismogenic volume is relatively large taking into account the high density of foci. The purpose of the present paper is to investigate source parameters and clustering properties for the repetitive earthquakes (located close each other) recorded in the Vrancea seismogenic subcrustal region. To this aim, we selected a set of earthquakes as templates for different co-located groups of events covering the entire depth range of active seismicity. For the identified clusters of repetitive earthquakes, we applied spectral ratios technique and empirical Green's function deconvolution, in order to constrain as much as possible source parameters. Seismicity patterns of repeated earthquakes in space, time and size are investigated in order to detect potential interconnections with larger events. Specific scaling properties are analyzed as well. The present analysis represents a first attempt to provide a strategy for detecting and monitoring possible interconnections between different nodes of seismic activity and their role in modelling tectonic processes responsible for generating the major earthquakes in the Vrancea subcrustal seismogenic source.

Source Parameter Variability of Intermediate‐Depth Earthquakes in Japanese Subduction Zones

“…In a different kind of intermediate‐depth earthquake setting, Prieto et al () find a strong scaling of stress drop with magnitude in the Bucaramanga Nest ( ); however, earthquake nests are anomalous, highly concentrated clusters of seismic activity that may not represent typical subducting slab behavior. The extant earthquake nests themselves also appear to behave differently, with evidence for thermal shear runaway in the Hindu Kush (Poli et al, ), but no significant scaling of source parameters in the Vrancea Nest in Romania (Popescu et al, ). Ichinose et al () studied historical instraslab events in the Cascadia subduction zone and concluded that those events occurred on smaller areas with high stress drops.…”