Earthquake mechanism and characterization of seismogenic zones in south-eastern part of Romania

Abstract

Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998-2012 time interval. The catalogue is limited geographically to the Carpathians Orogeny and extra-Carpathians area located in the southeastern part of Romania because similar investigations cover the rest of the country. The catalogue comprises 259 intermediate-depth seismic events and 90 crustal seismic events, recorded in the considered time interval with acceptably constrained fault plane solutions (minimum 10 reliable polarities, small ratio of rejected polarities versus input polarities and non-zero focal depth). We use specific graphical tools in order to emphasize statistically representative features of the stress field as coming out from our results. The fault plane solutions of the Vrancea earthquakes generated in a confined sinking plate in the mantle reflect the dominant geodynamic process in the study region. The typical features revealed by all the previous studies on the subcrustal seismic activity (predominant dip-slip, reverse faulting, characterizing both the weak and strong earthquakes) are reproduced as well by our investigation. As concerns the earthquake activity in the crust, a few new refined aspects are highlighted in the present work: (1) a deficit of the strike-slip component over the entire Carpathians foredeep area, (2) different stress field pattern in the Făgăraş-Câmpulung zone as compared with the Moesian Platform and Pre-Dobrogean and Bârlad Depressions, (3) a larger range for the dip angle of the nodal planes in the Vrancea subcrustal source, ~ 40°-70° against ~ 70°, as commonly considered.

Earthquake Source Properties of a Lower Crust Sequence and Associated Seismicity Perturbation in the SE Carpathians, Romania, Collisional Setting

“…All the fault plane solutions are well constrained by the selected seismic recordings. In addition, the focal mechanisms determined using both methods are comparable, increasing their reliability degree, and are also in agreement with the results pointed out within the study area by past studies [54][55][56]. For the mainshock, the fault plane solution indicates normal faulting with both nodal planes NW-SE oriented, in the direction of the Peceneaga-Camena Fault zone.…”

Present-day stress field pattern in the Vrancea seismic zone (Romania) deduced from earthquake focal mechanism inversion

“…In the present study we computed the stress field pattern in the Vrancea area by inverting the earthquake focal mechanisms using an extended and complete set of fault-plane solutions available for the Vrancea intermediatedepth and crustal earthquakes recorded between 1929 and 2012 [Radulian et al, 2018[Radulian et al, , 2019.…”

“…The purpose of the present study is to employ a comprehensive set of fault-plane solutions available for the Vrancea intermediate-depth and crustal earthquakes [Bala et al, 2019] in order to emphasize the stress characteristics in the subducted lithosphere and overlying crust in connection with the geodynamic processes responsible for generating the seismicity at the South-Eastern Carpathians Arc bend. The dataset comprising of a catalogue of fault-plane for the earthquakes recorded between 1929 and 2012 [Radulian et al, 2018;2019] called REFMC [Radulian et al, 2020] is much better represented both in number of events and quality (considering the number of stations used but also in some cases the method of determination), comparatively with previous investigations [Radulian et al, 2000;Radulian et al, 2002]. The improved data allow us to estimate the stress within the earthquake-prone descending body and in the overlying crust by inverting focal mechanism data in order to find the horizontal stress and to explore its distribution in depth.…”

“…A catalogue of fault plane solutions for earthquakes recorded in Romania between 1929 and 2012 was compiled from the catalogues previously published by Radulian et al [2018] for the time interval 1998 for the time interval 1929 -2000. The contiguous catalogue of fault plane solutions (1929 -2012) is analyzed and presented in Bala et al [2019] separated in two groups: the intermediate-depth earthquakes occurring in Vrancea zone (VNI) at depths ≥ 50 km and the crustal earthquakes at depths < 50 km located above the subcrustal source, mostly in the southern part of Romania (Figure 1).…”

Designing and building earthquake warning system with Arduino and web-based SES60 SLP sensor

“…ATmega328 also acts as a serial communication channel via USB and as a port virtual com for software on computers. ATmega328 also supports I2C (TWI) and SPI communication [23]. Parameters which support this system are such as ADC, power amplifier where speaker output is the output of the signal amplified, and the gain section is for regulating the incoming signal following the sensitivity of the power amplifier [24], alarm where sirens usually have a certain type of sound [25], JavaScript can embed the encoding in an HTML document or a single application [26], [27], and MySQL software is the ability to handle large amounts of data [28], [29].…”