Strong earthquakes in Azerbaijan for historical and contemporary periods (conceptual review)

Based on the results of the study of literary and archival primary sources, the paper clarifies the available information about catastrophic and destructive earthquakes in Azerbaijan for the historical period with a magnitude of M≥6. Among the strong historical earthquakes in Azerbaijan there are the following: earthquakes in 427, the Ganja (Goygol in 1139), the Ganja in 1235, the East Caucasian in 1667 (± 1 year), the Mashtaga (1842), numerous Shamakhi earthquakes (1192, 1667, 1668, 1669, 1828, 1859, 1868, 1872, 1902), Ardebil (1924), Lankaran (1913), Caspian earthquakes (957, 1812, 1842, 1852, 1911, 1935, 1961, 1963, 1986, 1989, 2000), which caused both changes in the relief of the Earth’s surface, and the destruction of buildings and numerous human casualties. The background seismicity was investigated based on the results of continuous instrumental observations for the period 1902—2019. Seismic processes are unevenly distributed on the territory of Azerbaijan. Existing catalogs of seismic events have been investigated. The behavioral changes in seismicity parameters have been studied. An overview conceptual analysis of two main methods for assessing seismic hazard is given: probabilistic and deterministic, which have found their wide application in recent decades. In conclusion, the most important and general tasks of future seismological studies are emphasized, which are to be performed in the next decades.

Seismic hazard and seismicity parameters in southwestern Alborz

Alborz Province is located west of Tehran Province on the South Alborz seismic belt. Geological and seismological analyses within a radius of 200 km from the center of Karaj identified five seismic zones and seven linear seismic sources. The maximum magnitude was calculated for the seismic zones using available correlations. The Kijko and Sellevoll (1992) method was used to calculate seismicity parameters, and the graphs of the return period and the probability frequency of recurrence of the earthquake magnitude in each zone were plotted for the 475-year return period. According to the calculations, the highest and lowest earthquake magnitudes of 7.6 and 6.2 were respectively obtained in Zones 1 and 4.

Seismicity Parameters Analysis In Space-Time Distribution For Northeast India.

A complete homogeneous earthquake catalogue is prepared to estimate seismicity parameters and their spatial-temporal variation in nine seismogenic source zones for Northeast India. The value of seismicity parameters like a-value, b-value, and MC value i.e., 7.37, 0.93(± 0.013), and 4.6, respectively have been estimated from the frequency-magnitude distribution. Moreover, the maximum-likelihood method has been utilized to map the spatial variation of the above parameters. The spatial variation of low b-values is dominant in the Indo-Burman Range, the Main Boundary Thrust, and the vicinity of the Sagaing fault. High seismic activity rate has been obtained in the Indo-Burman range as observed from spatial variation of a-value parameter. Furthermore, the return periods and the annual probability of an earthquake have been calculated for each zone. The results of this seismicity parameter provide useful information about the hazard level of a particular zone and further helps in preparing the hazard map of Northeast India.

Identifying the main factors that control Probabilistic Seismic Hazard Assessment (PSHA) in the Aegean area: Results from OFAT (One Factor at A Time) analysis

<p>The broader Aegean area is one of the highest seismicity regions in Europe, with almost half of the European seismicity released in this region, often with damaging mainshocks, such as the recent <strong>M</strong>7.0 Samos event. While several Probabilistic Seismic Hazard Assessment (PSHA) studies have been performed for this area, an attempt to quantify the main factors controlling PSHA has not been performed. To study the effect that each input factor (seismic source model, GMPE, seismicity parameters, etc.) has on the seismic hazard calculations, an <strong>OFAT</strong> (One Factor at A Time) analysis has been conducted. For this analysis we considered two standard peak ground motion parameters, PGA and PGV, for a typical PSHA scenario, namely 10% probability of exceedance for a mean return period of 50 years (equivalent to a 476 yr return period). For the analysis the following factors were considered: a) Four (4) seismicity area-type source models for the broader Aegean area (Papazachos, 1990; Papaioannou and Papazachos, 2000; Woessner et al., 2015; Vamvakaris et al., 2016), as well as various uncertainties for the associated G-R seismicity parameters and active fault geometries of each seismic source, b) ten (10) Ground Motion Prediction Equations (GMPEs), which contain four NGA-West2 (Abrahamson et al., 2014; Boore et al., 2014; Campbell and Bozorgnia, 2014; Chiou and Youngs, 2014), two European (Bindi et al., 2011; Cauzzi and Faccioli, 2008) and four “Greek” (Theodulidis and Papazachos, 1992; Skarlatoudis et al., 2003; Danciu and Tselentis, 2007; Chousianitis et al., 2018) equations, as well as a variable number of sigma for each equation and, c) the minimum (Mmin) and maximum (Mmax) source magnitude of each seismic source. Tornado diagrams (Howard, 1988) were generated for 42 selected sites of seismological interest that span the study area, allowing to explore the extent of each factor’s effect on the PSHA results. The sensitivity analysis results suggest that the GMPE selection, as well as uncertainties in the G-R parameters <strong>a</strong> and <strong>b</strong> are the most critical factors, significantly affecting the PGA/PGV levels for all sites. They also reveal a strong correlation of PSHA sensitivity with other seismicity parameters. For example, the employed source model and Mmax play a more critical role for regions of low seismicity, while the least important factor is the selected Mmin. The spatial distribution of the PSHA sensitivity on the various factors considered was also examined through the generation of several maps, exposing regions of high and of low PSHA uncertainty. The results can be efficiently employed by scientists and engineers in order to focus research and application efforts for a targeted uncertainty minimization of the most critical factors (which may not be the same for all sub-regions of the examined Aegean area), as well as to evaluate the reliability and uncertainty of the current PSHA estimates that are employed in seismic design.</p>

Seismic activity in stable continental regions

<div> <p><span>Stable continental regions (SCRs) have low seismicity and large magnitude earthquakes are infrequent and diffuse compared to plate boundary settings. Because of this, seismicity parameters required for seismic hazard analysis (SHA) are difficult to constrain. A method to overcome this challenge involves using an analogue approach to generate seismic hazard inputs in SCRs. Seismic hazard analysis of these regions develops recurrence parameters by drawing upon data from a larger global database than what is typically done for plate boundary regions. This is completed by choosing regions that are considered seismotectonically analogous and then amalgamating data from the regions to generate larger and perceivably more robust seismicity data sets. Historically, this is done by considering all SCRs as analogous and including all of their data into the analysis. </span></p> <p><span>This study refines and updates this approach by assessing whether there is internal variability of seismogenic potential within SCR crust that can be distinguished by comparing properties of the crust to seismicity. We completed this analysis by: (1) compiling a global homogeneous earthquake catalog for earthquakes >= Mw 2 up to July 2020 which includes historical and instrumental events; (2) subdividing global SCR crust into five geological domains that distinguish crustal criteria within SCRs; (3) calculating and comparing the seismic parameters between the different SCRs and sub-domains to better understand the range in values across different SCRs and determine if there is statistically observable variation between sub-domains</span>. <span>Our results provide an initial step towards redefining what crustal characteristics define analog regions for use in seismic hazard studies.</span></p> </div>

Development and characterization of a seismic source model for the Jalisco-Colima-Michoacán region, Western Mexico

<p>The Mexican subduction zone, the Gulf of California spreading center, as well as the triple junction point around the Jalisco and the Michoacán Blocks, represents the most active seismogenic belts inducing seismic hazard in the Jalisco-Colima-Michoacán region. Herein, considering such seismotectonic setting, we have developed a new seismic source model for the surrounding of this zone to be used as an input to the assessment of the seismic hazard of the region.</p><p>This new model is based on revised Poissonian earthquake (1787-2018) and focal mechanism (1963-2015) catalogs, as well as crustal thickness data and all information about the geometry of the subducting slabs. The proposed model consists of a total of 37 area sources, comprising the three different possible categories of seismicity: shallow crustal, interface subduction, and inslab earthquakes. A special care was taken during the delimitation of the boundaries for each area source to ensure that they represent a relatively homogeneous seismotectonic region, and to include a relatively large number of earthquakes that enable us to compute, as reliable as possible, seismicity parameters.</p><p>Actually, the sources zones were delimited following the standard criteria of assessing a probabilistic seismic hazard, being characterized in terms of their seismicity parameters (annual rate of earthquakes above Mw 4.0, b-value, and maximum expected magnitude), mean seismogenic depth, as well as the predominant stress regime. The proposed seismic source model defines and characterizes regionalized potential seismic sources that can contribute to the seismic hazard at the Jalisco-Colima-Michoacán region, providing the necessary information for seismic hazard estimates.</p>