Earthquake

Analysis of dynamic soil properties: shaking table testing

This paper presents an analysis of shaking table tests on wrap-faced embankments situated on soft clay. The model embankment was placed in a laminar box mounted on a shaking table. The results from these tests were verified through numerical analysis. Different model tests were conducted with varying surcharge loads and acceleration levels. It was observed that the response of the embankment on soft clay was significantly influenced by the base acceleration levels and the magnitude of the surcharge pressure. Data from the Loma Prieta earthquake (1989) was utilized in this experiment. The effects of various parameters on the acceleration response at different eleva-tions of the embankment and face deformations were also examined. The results indicate that the proposed wrap-faced embankment demonstrates significant resistance to earthquakes, particularly those similar to the Loma Prieta event, and provides an indicative performance measure of the wrap-faced embankment on soft clay soil.

Possible locations of strong earthquakes in western Tan Shan

The occurrence of earthquakes depends on a variety of factors generating various anomalies that are used as earthquake precursors. Mathematical modeling of the stress-strain state of the Earth's crust, verified with available instrumental data, can be used to determine the possible locations of tectonic earthquakes. For this purpose, the stress-strain state of the earth's crust of the West Tien Shan microplate has been modeled. The modern movements of the Earth's crust are modeled using the hydromechanics equations of creep motion (Stokes equations). Known GPS data served as boundary conditions. For a number of reasons at this time it is difficult to solve three-dimensional continuum equations for the Earth's crust (not exact structure of crust layers, their physical properties, etc.). Since the strong earthquakes in the region under consideration occur at depths of 15-20 km, we decided to estimate the average stress state for these depths. The Stokes equations were averaged over depth. The averaged two-dimensional Stokes equations are solved by boundary element methods. Isolines of maximum tangential stresses are constructed. Together with the energy criterion of strength, they served to determine the locations of critical stresses in the Earth's crust, where earthquakes are possible. The main horizontal stress vectors σ1, σ2 are constructed from the averaged stresses σxx, σxy, σyy. With the addition of lithostatic pressure as the third component of the main vector σ3=σver, the geodynamic state of the Earth's crust was evaluated using Anderson's method.

Looking into the quite unexpected and catastrophic Morocco Earthquake: time for resilience

There was a significant seismic event (MW 6.8) that occurred in Morocco during the evening of Friday, September 8, 2023. It resulted in the loss of numerous lives, injuries to a substantial number of individuals, and severe destruction to rural communities near the southern metropolis of Marrakesh. This earthquake is regarded as one of the most lethal in the nation's recent history. The earthquake was quite shallow at a depth of 19 km. According to Moroccan state television, the interior ministry reported that the number of fatalities has risen to 2,946, primarily concentrated in the hilly Al Haouz region. Additionally, there have been 5,674 reported cases of injuries. This concise work reports the seismicity as well as tectonic settings of the region. Apart from this, the attributes of damage are also briefly overviewed along with final comments on disaster resilience.

On the study of anomalous variations of the geomagnetic field

Elucidation of the nature of anomalous variations of the geomagnetic field throughout the geological and modern periods is important for identifying local anomalies associated with the preparation of strong earthquakes. The results of detailed studies of geomagnetic field variations over the past 100 years reflect the manifestation of anomalies in a wide spatiotemporal spectrum, intensity and shape. In terms of their parameters, they are comparable to the anomalous variations caused by the processes of preparation of strong (M ≥ 5) earthquakes. As a result of a review of the literature, it was found that the period of secular variations of the geomagnetic field according to paleomagnetic data ranges from 600 to 100 thousand years. According to the archaeomagnetic data, abnormal fluctuations of the geomagnetic field with a period of several decades to 8-9 thousand years have been revealed. Measurements of the geomagnetic field over the past 200 years have revealed abnormal fluctuations with periods from 10-15 days to 20-60 years. The main versions about the possible nature of the age-old variations manifested in the geological past and present are given.

A new insight view to the strong (М7.2 and М7.8) earthquakes of 1904 in Bulgaria

The Kresna-Kroupnik seismic source (SS K-K) is under deep investigation. This source is famous with the occurrence of two very strong earthquakes (M7.2 and M7.8) on 4th April 1904 in a time domain of 20 minutes, thus considered to be a “doublet”. A short review of the European seismicity shows that during the last 200 years there is not so strong seismic event on the territory of continental Europe. Besides its power this “doublet” demonstrated a numerous peculiarities which do not fit the recent knowledge about the surface expression of such powerful seismic event. The very short length of the surface dislocation (less than 40 km), the relatively small area of high intensities (up to X-XI EMS), the large area of felt effects, the large area of liquefaction, etc., do not coincide with the recent observations of similar earthquakes (for example Kahramansharah-Gasientep on 6th February 2023). All these strange peculiarities triggered a wide interest to seismologists to study in depth the behavior of the SS K-K. We started with deep insight view to the low velocity layer established by us earlier at depths of 50 to 150 km. Then proceed up by seismic tomography for the depth interval 0-50 km, considered as a thickness of Moho and finally reach the recent GNSS measurements in the area to reveal how and why the SS K-K produced such effects by the earthquakes of 1904. Following the concept of the protrusion of the low velocity body just under the source, than the logic of existence of vertical blocks at shallow depths with different geophysical characteristics (lower and higher P and S waves velocities), thermal and Bouguer gravity anomalies and finally expanding our knowledge by the GNSS displacements of the surface layers which show the behavior of the recent stress field. Thus we were able to create an algorithm explaining the geodynamic environment of the SS K-K observed peculiarities without visible logical contradictions.

Analysis of hydrogeoseismological anomalies observed in groundwater during earthquakes

This bibliometric analysis aims to research articles, conferences, and books published on groundwater hydrochemical anomalies due to earthquakes during 1970-2024 in fourteen seismically active countries. The data used in this analysis were obtained from the online version of the Scopus database and corresponded to 379 publications according to the selection criteria. Bibliometric analysis showed that all articles were published in English, with the most publications coming from Japan, India, Germany, China, Turkey, Taiwan, Italy, the Russian Federation, and the United States.