Possible Triggered Seismicity Signatures Associated with the Vrancea Intermediate-Depth Strong Earthquakes (Southeast Carpathians, Romania)

Abstract

Online Material: Vrancea earthquake catalogs. To date, no generally applicable procedure is available for distinguishing triggered earthquakes from other seismic events that occur, apparently randomly, within a certain region (see discussion in van der Elst and Brodsky, 2010). In particular, it is not habitual to utilize diagrams illustrating the time evolution of the seismic release (e.g., Mantovani et al. , 1987; Husen et al. , 2004) as a diagnostic tool. However, that investigation method has been shown in the present study to be outstandingly useful for highlighting similarities existing between the patterns of seismic activities recorded in two distinct and possibly interacting lithospheric domains associated with the Carpathians orogenic belt in Romania. The main potentially causative earthquakes occurred in the Vrancea seismic zone (hereafter VSZ), located at intermediate depths (60–180 km) beneath the southeast Carpathian Arc bend (Fig. 1), whereas the resulting seismicity enhancements (recorded several months to tens of months afterward) developed at less than 60 km depth in the adjoining Carpathians‐foredeep region. The concerned Carpathians Mountains foreland basement is built up of two distinct lithospheric plates: the east European plate to the north‐northeast and the Moesian plate to the south‐southwest (Fig. 1), which are separated by a regional system of northwest–southeast‐oriented fractures (the so‐called Trotus and Peceneaga‐Camena faults). In coincidence with that contact, a shallow seismicity domain, designated (Raileanu et al. , 2007) as the Marasesti–Galaţi–Braila lineament (hereafter MGBL), has also been delineated. Figure 1. General seismotectonic setting of the considered area (geology after Sandulescu, 1984). The Carpathian Mountains accretionary wedge has overthrust (saw‐tooth boundary) the corresponding foreland, which extended on two major plates (east European and Moesian). The roughly oval, solid contour bounds the epicentral domain of the intermediate‐depth (≥60 km) Vrancea earthquakes. Large black symbols …