Assessing and improving focal mechanisms in Switzerland: Towards a comprehensive seismotectonic model of the Central Alps and their foreland

<p>Seismotectonic models that combine all the relevant seismotectonic data (e.g., hypocenter locations and velocity models, focal mechanisms and moment-tensors, faults, geodetic data, and in-situ/regional stress data) constitute a pre-requisite to better understand the interplay between stress, faulting and seismicity of a region. This study is a contribution to the multiannual project SeismoTeCH funded by the Swiss Geophysical Commission (SGPK) and coordinated by the University of Bern to produce an integrative seismotectonic model for the entire territory of Switzerland. In this context, our aim is to provide an up-to-date, high-quality, and consistent catalog of first-motion focal mechanisms computed by the Swiss Seismological Service (SED) since 1976. For this purpose, we developed a quality classification scheme for existing mechanisms based on a priori independent information (mainly applied to the oldest mechanisms in the catalog) combined with statistical methods such as HASH (Hardebeck and Shearer, 2002) and probabilistic source mechanisms scanner algorithms (Massin and Malcom, 2018) to probe the solution space and translate probability density functions to a discrete quality rating.</p><p>Tests on selected problematic mechanisms are also carried out in order to assess the sensitivity of the focal mechanisms to the velocity models used to calculate location and take-off angles. In particular, we compare existing solutions using the standard 3D P-wave model of the SED with solutions based on recently derived high-resolution 3D Pg+Sg models. These tests are functional to understand the benefits of developing an updated full crustal velocity model for first-motion focal mechanisms calculations, in particular in relations to the focal depths and the accuracy of take-off angles.</p><p>Finally, to improve the completeness of the existing catalog, we explore new methodologies that would incorporate automated (possibly real-time) and semi-automated techniques for expanding the calculation of first-motion focal mechanisms (and moment tensors) to events of smaller magnitude. The Anzere/Sanetschpass sequence of November 2019 is used to assess and develop these new methods. As a preliminary result of these combined efforts, we present here a high-resolution map of strain-based deformation across Switzerland. This work represents a benchmark for future regional-scale stress inversion and sets the basis for the development of a consistent, fully accessible, and dynamic focal mechanisms database for Switzerland.</p>

Active faults of the Kerch’s Peninsula: new results

In the paper there are results of a recent study of the active faults in the Kerch Peninsula. There was compiled a Map of Active Faults - sources of the strong earthquakes occurred in Late Holocene. The map is a regional seismotectonic model of strong earthquake sources - detailed basis for a spatial prognosis of the seismic hazard. Results of the study show that the Kerch Peninsula demonstrates signs of the classical morphostructures, and a morphology of the modern peninsula contours is caused by the large active fault zones.

SEISMOTECTONICS OF THE KERCH-TAMAN REGION DESTRUCTIVE EARTHQUAKES

Рассмотрена сейсмотектоническая модель Керченско-Таманского района Крымско-Кавказского сейсмического пояса. Характерной чертой Керченско-Таманского сейсмического района является наличие разрушительных исторических землетрясений с М = 6,0–7,5 и интенсивностью до 9 баллов при отсутствии сильных сейсмических событий в инструментальный период. Эпицентры известных разрушительных землетрясений локализованы в южной части Азовского моря и в акватории Керченско-Таманского пролива, а их гипоцентры находились на глубине 15–40 км в консолидированном слое земной коры Индолокубанского блока Скифской плиты, которая Крымским и Западнокавказским разломами отделена от южнее расположенной Восточно-Черноморской плиты. Descriptions are given of the seismotectonic model of the Kerch-Taman region of the Crimean-Caucasian seismic belt. A distinctive feature of the Kerch-Taman seismic region is the existence of destructive historical earthquakes with M = 6,0–7,5 and intensity of up to 9 points in the absence of strong seismic events during the instrumental period. Epicenters of known destructive earthquakes are located in the southern part of the Azov Sea and in the Kerch-Taman Strait water area, and their hypocenters were located at the depth of 15–40 km in the consolidated layer of the Earth's crust of the Indolokuban block of the Scythian plate, which is separated by the Crimean and West Caucasian faults from East-Black Sea plates situated to the south.

A seismic source zone model for the seismic hazard assessment of Slovakia

We present a new seismic source zone model for the seismic hazard assessment of Slovakia based on a new seismotectonic model of the territory of Slovakia and adjacent areas. The seismotectonic model has been developed using a new Slovak earthquake catalogue (SLOVEC 2011), successive division of the large-scale geological structures into tectonic regions, seismogeological domains and seismogenic structures. The main criteria for definitions of regions, domains and structures are the age of the last tectonic consolidation of geological structures, thickness of lithosphere, thickness of crust, geothermal conditions, current tectonic regime and seismic activity. The seismic source zones are presented on a 1:1,000,000 scale map.