Active Geological Structures Research Articles

Analysis of Magnitude–Frequency Distribution of Earthquakes in the Sichuan Basin, Southwest China

Abstract The Sichuan basin is characterized by underdeveloped active geological structures and low seismic activities. In recent years, an increase in seismicity has been observed in the southern Sichuan basin, which includes small earthquakes induced by water injection during shale gas exploitation and M ≥ 5.0 earthquakes, causing unexpected damage and casualties. This necessitates a comprehensive analysis of the magnitude–frequency distribution of the current seismicity. In this study, we examined the current seismicity using instrumental earthquake records at different periods and estimated the temporal and spatial variations in b-value. We found that the b-values widely vary in the Sichuan basin and analyzed the spatial differences in b-value in seven different earthquake clusters. The results show that the intense fault movement on the western boundary of the Sichuan basin might be the main controlling factor of the increased seismicity in the southern basin instead of being induced by water injection. Furthermore, earthquakes in the Sichuan basin follow the same size distribution as the events on the boundary faults and the Sichuan–Yunnan rhombus active block. Thus, it is appropriate to consider the magnitude–frequency distribution of earthquakes for the Sichuan basin and the Sichuan–Yunnan rhombus block together rather than separately. These results may help improve the recurrence models in probabilistic seismic hazard assessment of the region.

Spatial Heterogeneity of b Values in Northeastern Tibetan Plateau and Its Interpretation.

The northeastern margin of the Tibetan Plateau (NE Tibetan Plateau) exhibits active geological structures and has experienced multiple strong earthquakes, with M ≥ 7, throughout history. Particularly noteworthy is the 1920 M81/2 earthquake in the Haiyuan region that occurred a century ago and is documented as one of the deadliest earthquakes. Consequently, analyzing seismic risks in the northeastern margin of the Tibetan Plateau holds significant importance. The b value, a crucial parameter for seismic activity, plays a pivotal role in seismic hazard analyses. This study calculates the spatial b values in this region based on earthquake catalogs since 1970. The study area encompasses several major active faults, and due to variations in b values across different fault types, traditional grid-search methods may introduce significant errors in calculating the spatial b value within complex fault systems. To address this, we employed the hierarchical space-time point-process (HIST-PPM) method proposed by Ogata. This method avoids partitioning earthquake samples, optimizes parameters using Akaike's Bayesian Information Criterion (ABIC) with entropy maximization, and theoretically allows for a higher spatial resolution and more accurate b value calculations. The results indicate a high spatial heterogeneity in b values within the study area. The northwestern and southeastern regions exhibit higher b values. Along the Haiyuan fault zone, the central rupture zone of the Haiyuan earthquake has relatively higher b values than other regions of this fault zone, which is possibly related to the sufficient release of stress during the main rupture of the Haiyuan earthquake. The b values vary from high in the west to low in the east along the Zhongwei fault. On the West Qinling fault zone, the epicenter of the recent Minxian-Zhangxian earthquake is associated with a low b value. In general, regions with low b values correspond well to areas with moderate-strong seismic events in the past 50 years. The spatial differences in b values may reflect variances in seismic hazards among fault zones and regions within the same fault zone.

Delineating geological structure utilizing integration of remote sensing and gravity data: a study from Halmahera, North Molucca, Indonesia

Halmahera Island is the result of the interaction between the Indo-Australian Plate, the Molucca Sea Plate, and the Philippine Plate, which gave rise to many active geological structures that are vulnerable to seismic activity around the island. The complexity of this geological structure makes Halmahera Island very interesting to study. This study aims to identify geological structures by integrating remote sensing and gravity satellite data. Surface lineament analysis using the remote sensing method was carried out based on Sentinel-1A imagery data. The gravity method uses GGMPlus satellite data to clarify the continuity of geological structures that cannot be clearly mapped on the surface. Lineament analysis on gravity data uses techniques such as fast sigmoid edge detection (FSED) and Euler deconvolution. The results of lineament interpretation based on integrating remote sensing and gravity satellite data show that the NE-SW structure controls the northern and northeastern arms of Halmahera.
 In contrast, the southern arm is dominated by the NW-SE structure. The Euler depth estimation shows that the Halmahera area contributes to having geological structures at various depths. Deep structures reach 4 km, while shallow structures are found at depths of up to 2 km. Earthquake hypocenter data strengthen the interpretation of this geological structure. This comprehensive study yields an excellent correlation between gravity and remote sensing techniques in describing the general structural framework of the area. The new finding is an NE-SW trending geological structure on the northern Halmahera arm, which may be caused by two different tectonics first, the subduction of the Molucca Sea Plate with the Halmahera Plate in the west. Second, the strike-slip movement is trending NE-SW, which cuts the northern and northeastern arms due to the rotational movement of the thrust fault with the Philippine Plate to the west.

Ecological monitoring of conditionally clean areas in Volgograd agglomeration

Introduction. The territories of conditionally clean zones are allocated for the development of collective gardens and summer cottages, being formed far from industrial centers in ecologically clean, picturesque places for healthy recreation of citizens. The purpose of the study is to assess the environmental condition of the territories of horticultural non-commercial partnerships (HNP) “Oroshenets”, “Shelf” (Volgograd) in a comparative analysis with the residential area of Srednyaya Akhtuba work settlement (Sredneakhtubinsky district of the Volgograd region), affected by industrial production using aerosol indicators.
 
 Materials and methods. The material of the study was aerosol suspensions prepared from particles, collected from the leaves of Prunus armeniaca L. in accordance with international methods (A. Lukowski, R. Popek et al., 2020) and studied in terms of acidity, electrical conductivity on electrochemical equipment of the “MULTEST” series (Russia); toxicants were identified based on the development of test objects (RF patent No. 2746764); analysis of the disperse composition of aerosols, their amount and mass fraction were carried out according to GOST R 56929–2016. Prediction of sources of natural pollution on the territory of HNP was carried out by the method of remote sensing of the Earth.
 
 Results. The Integral assessment of the ecological condition of the territory of the conditionally clean zone during 2018–2020 demonstrated 1 point (QSNT = 0.699–0.725). Mineralized aerosols (EC = 38.11–42.68 (μS/cm)) were steadily recorded in the atmospheric air, the amount of PM10 reached 70 %, while there were no acid impurities and toxicants.
 
 Conclusions. The ecological status of the HNP area was evaluated as an “ecological norm”, but “with slight changes in flora and fauna”, which indicated a slight pollution of the territory from possible natural sources in the form of active geological structures (projections of foci of surface temperature anomalies, confirmed by the data of the latest satellite systems (Landsat-8, USA) and field studies of “hot spots”).

Earthquake affects subsidence in Jakarta using Sentinel-1A time series images and 2D-MSBAS method

Excessive groundwater extraction has been well known as the main factor causing land subsidence in several cities in Jakarta Basin, Indonesia. This area is surrounded by active geological structures and has thick sediments. This study emphasizes the impacts of earthquakes on subsidence over Jakarta and its surroundings by using the Sentinel-1A images and 2D-MSBAS (Multidimensional Small Baseline Subset) method. Sixty-one ascending and 66 descending Sentinel-1A images were utilized to derive 121 deformation maps from 26 March 2017 to 2 July 2019 by using the 2D-MSBAS method. Linear and nonlinear displacement variations were analyzed to understand earthquake impacts on the subsidence and their seasonal characteristics. On 23 January 2018, the Mw 5.9 earthquake shaking off the coast of Java significantly affected ground surface subsidence in Jakarta. A cumulative magnitude and linear rate increase of the subsidence reached approximately -196 mm and -44 mm/yr, respectively, during the period of this study. Besides the subsidence rate changes, the earthquake also affected the expansion of the localized subsiding areas at several sites. The earthquake-activated fault affected the ground surface of the surrounding area, moving east and subsiding in the western part of the study area. Meanwhile, variations of the nonlinear subsidence to the seasonal precipitation depended on the aquifer system behavior to retain an elastic expansion and land cover types in the investigated regions.

СИЛЬНОЕ ЗЕМЛЕТРЯСЕНИЕ 05.02.2022 (ML 5.5) ВБЛИЗИ НЕФТЕГАЗОВОГО МЕСТОРОЖДЕНИЯ НА СЕВЕРО-ВОСТОЧНОМ ШЕЛЬФЕ О. САХАЛИН

On 5 February, 2022 at 21:18 UTC (February 6 at 08:18 local time), an earthquake of local magnitude ML = 5.5 with a hypocenter in the upper crust occurred on the shelf of northeastern Sakhalin. The earthquake was caused by slip on the Piltun-Chaivinsky fault, which until recently was not considered a seismogenic source. The studied earthquake located in the area with Coulomb stress increment caused by the catastrophic 1995 Neftegorsk earthquake is most likely tectonic in origin. The accumulated tectonic stress associated with static stresses, triggered by the strongest earthquake in the northeast of the island, caused east-dipping reverse fault displacements. The focal mechanism of the earthquake is characterized by near-horizontal compression axes oriented sublatitudinally. The authors pioneered in collecting and analyzing instrumental data on strong ground motions near an earthquake, which are of value for engineering seismology. The macroseismic data incorporating the information received from local residents via the Internet were analyzed. Findings of the study are of practical relevance, since each year economic activities related to the subsoil development are expanding and intensifying. The present knowledge of active geological structures of the Sakhalin shelf contributes to the reassessment of seismic hazard in gas and oil producing areas.

The role of active geological structures in forming hot springs in Ramsar, Iran

The hot springs of Ramsar, Iran are located at the northern zone of the Central Alborz Mountain Range along the Caspian Fault. Ramsar is a well‐known area with amongst the world's highest levels of natural radiation. Due to the local geology, which includes high levels of radium in rocks, soils, and groundwater, Ramsar residents are also exposed to high levels of alpha activity in the form of ingested radium. Nine springs were selected from the hot springs of Ramsar for this research, and water samples were tested to find the amount of dissolved materials and elements. Analysis of the results suggests that the hot springs of Ramsar originated from the sea. The results indicate that coincident with subduction of the southern Caspian basin and obduction of the Central Iranian crust over the southern Caspian crust, saline seawater reaches fracture zones of the Caspian Fault where it is heated due to mixing with radioactive materials and release of radon as a result of activity of the faults and its decay into radium. Then it migrates along the Caspian thrust faults and forms hot springs originated from regional surface waters of Ramsar. Those hot springs located next to thrust faults were the result of collision, and the origin of neighbouring cold springs is karst.

Elusive active faults in a low strain rate region (Sicily, Italy): Hints from a multidisciplinary land-to-sea approach

Low Strain Rate regions (LSRrs), i.e., areas undergoing tectonic deformation at rates of 1 mm/yr or less, often host important cities and highly vulnerable anthropogenic assets, and due to their subdued topography and relatively infrequent seismicity, are often considered low seismic hazard areas. Despite this, infrequent but high-magnitude earthquakes in such regions suggest that identifying active structures in the LSRr is one of the primary challenges for both the scientific community and modern societies. In such regions, one of the main issues in identifying active faults is the lack of valuable outcrop data due to erosional/sedimentation rates overwhelming the fault deformation, causing the hidden morphological signature of the tectonic structures.This work proposes a multidisciplinary approach designed to detect active geological structures and their related deformation in such areas. Our approach consists of quantitative morphotectonic, offshore and onshore tectonostratigraphic and GNSS joint analyses. To test this approach, we selected as a natural laboratory the partially offshore northern Sicilian LSRr (southern Italy) in the coastal sector located between the two major cities of Palermo and Termini Imerese. This area includes the compressional structures of the northern sector of the Apennine-Maghrebian fold and thrust belt, presently accommodating the slow Africa-Europe plate convergence.The main results we achieved are 1) new evidence of active tectonic deformation in this region; 2) the 3D modelling of two NNW-trending active faults; 3) the slip rate of a segment of the westernmost of the two detected faults; 4) a newly recorded relative GNSS velocity field; 5) a new morphotectonic map and morphotectonic evolution model of the study area. Our multidisciplinary approach allowed us to shed new light on the active tectonic framework of a slowly deforming area that crosses the physical limit of the coastline.

Tsunami potential source in the eastern Sea of Marmara (NW Turkey), along the North Anatolian Fault system

Based on morphobathymetric and seismic reflection data, we studied a large landslide body from the eastern Sea of Marmara (NW Turkey), along the main strand of the North Anatolian Fault, one of the most seismically active geological structures on Earth. Due to its location and dimensions, the sliding body may cause tsunamis in case of failure possibly induced by an earthquake. This could affect heavily the coasts of the Sea of Marmara and the densely populated Istanbul Metropolitan area, with its exposed cultural heritage assets. After a geological and geometrical description of the landslide, thanks to high-resolution marine geophysical data, we simulated numerically possible effects of its massive mobilization along a basal displacement surface. Results, within significant uncertainties linked to dimensions and kinematics of the sliding mass, suggest generation of tsunamis exceeding 15–20 m along a broad coastal sector of the eastern Sea of Marmara. Although creeping processes or partial collapse of the landslide body could lower the associated tsunami risk, its detection stresses the need for collecting more marine geological/geophysical data in the region to better constrain hazards and feasibility of specific emergency plans.

Antecedent topography and active tectonic controls on Holocene reef geomorphology in the Great Barrier Reef

The Great Barrier Reef is generally considered a passive tectonic setting, however the effect of antecedent topography and local geological structures on Holocene reef development is poorly understood. Offshore reefs along the central shelf were recently hypothesized to have grown continuously through a possible small Holocene sea level fall, in response to greater local subsidence, in contrast to reefs immediately to the north and south, which experienced synchronous turnoff phases. We tested this hypothesis by isolating four map zones along the GBR shelf and using: (1) a geomorphic reef type classification applying perceived evolutionary “age” as juvenile, mature, and senile domains based on geomorphology; (2) analysis of bathymetry data to understand the role of antecedent topography on the spatial distribution of reef type domains and general sea floor depths; and (3) the distribution of earthquake epicentres as an indication of possible active geological structures (i.e., faults). The results reveal that juvenile reefs (42.25 %) are more abundant in the central shelf, whereas mature-2 (40 %) and senile (31 %) reefs are more abundant in the northern zone. In the south-central zone, mature-2 reefs are prevalent, while the southern zone includes a mixture of juvenile and mature to senile domains with a sharp internal boundary. These results support the hypothesis that the central zone may have experienced greater active subsidence during the Holocene. Bathymetric data support greater regional subsidence in both central and south-central zones, but reefs are less abundant and cover a lesser percentage area of their antecedent platforms in the central zone, consistent with greater subsidence there. The boundaries between the central zone and adjacent zones are the sites of clusters of recent earthquakes, consistent with the occurrence of active geological faults bounding the zone of greater Holocene subsidence. Combined, our data support the occurrence of a tectonically defined region of active greater subsidence in the central GBR shelf that has affected the geomorphology and growth history of reefs through the Holocene. Knowledge of such spatial partitioning of reef behaviour may allow reef managers to better suite their efforts to local conditions, especially in regard to predicted sea level rise, while highlighting potential seismic risks over longer time frames.

Assessment of Seismogeodynamic Activity of Mining Areas on the Basis of 3D Geoinformation Modeling

The article deals with the creation of an information and analytical platform for assessing external causes of technogenic (man-made) accidents and for improving methods of their predication and prevention on the territories of long-term geological, mining, and engineering activities on the Southeastern (SE) Transbaikal region example — one of the key areas for mining and extraction of the strategic raw minerals in Russia. 3D modeling of active geological structures and hazardous seismogeodynamic processes on GIS-based technologies is a key instrument for forecasting dangerous natural and technogenic events and risk reduction of their occurrence. A matter of minimizing consequences of natural and technogenic disasters for such facilities of increased technological and environmental hazards as minefields, radiochemical facilities, sites for spent nuclear material disposal, dams, gas and oil pipelines, etc. has become essential. It is necessary to assess modern geodynamic territory’s activity on a unified geoinformation platform applying the newest integrated geological-geophysical researches’ methods for these objects, to select seismically active fault-fracture zones, to determine the rate and direction of surface displacement, to establish patterns of subsoil stressed-strained state natural component influence on behavior of local technogenic processes. Taking into account the specificities of geotectonic structure of mining territories, the structure of monitoring seismogeodynamic processes network on multifunctional geodynamic test sites should be developed. Observations made on test sites form the information basis for forecasting of lithosphere condition, taking decisions on rational subsurface management and providing ecological safety of the territory.

Connecting subduction, extension and shear localization across the Aegean Sea and Anatolia

SUMMARY The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African, and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction, but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geological structures. We find that tectonic escape is facilitated by a plate-boundary-like, trans-lithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north–south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa–Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8 mm yr–1 in a largely trench-normal direction except near eastern Crete where variably oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy–Pliny–Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation.

Applying primary data from permanent stations for geodynamic zoning

Introduction. The article focuses on present-day geodynamic motion in order to carry out geodynamic zoning of territories. Geodynamic monitoring may be both regional, for instance, of the Russian Federation, Ural region, geological rock mass, and it may also be local, i.e. covering a deposit and enclosing rock mass. Permanent stations of Global Navigation Satellite System (GNSS) have been used as a source of data for deformation monitoring. Methodology included the method of visualizing geodynamic motions according to the results of cyclic geodetic measurements which makes it possible to single out active geological structures, blocks, and tectonic faults on reasonable grounds. Results. It has been shown that it is advisable to use not modules of observation station displacement vector values but their velocities reduced to an annual cycle as a key source of information on geodynamic motion at large spatial-temporal bases. It has been indicated that an important characteristic of geodynamic motion vector field is divergence which characterizes the degree of convergence or divergence of a vector flux. Summary. Basic theses have been identified of the method of present-day geodynamic motions monitoring and visualization in the form of a vector field according to the results of cyclic geodetic measurements. Based on experimental data, it has been determined that the present-day geodynamic motion is vortical being the indicator of active tectonic faulting.

New seismological data from the Calabrian arc reveal arc-orthogonal extension across the subduction zone

The Calabrian Arc subduction-rollback system along the convergent Africa/Eurasia plate boundary is among the most active geological structures in the Mediterranean Sea. However, its seismogenic behaviour is largely unknown, mostly due to the lack of seismological observations. We studied low-to-moderate magnitude earthquakes recorded by the seismic network onshore, integrated by data from a seafloor observatory (NEMO-SN1), to compute a lithospheric velocity model for the western Ionian Sea, and relocate seismic events along major tectonic structures. Spatial changes in the depth distribution of earthquakes highlight a major lithospheric boundary constituted by the Ionian Fault, which separates two sectors where thickness of the seismogenic layer varies over 40 km. This regional tectonic boundary represents the eastern limit of a domain characterized by thinner lithosphere, arc-orthogonal extension, and transtensional tectonic deformation. Occurrence of a few thrust-type earthquakes in the accretionary wedge may suggest a locked subduction interface in a complex tectonic setting, which involves the interplay between arc-orthogonal extension and plate convergence. We finally note that distribution of earthquakes and associated extensional deformation in the Messina Straits region could be explained by right-lateral displacement along the Ionian Fault. This observation could shed new light on proposed mechanisms for the 1908 Messina earthquake.

Nonlinear stress wave generation model as an earthquake precursor

A network of vertical static pendulums (tiltmeters) has been in operation in Central Europe since July 2007. Hundred and eighty three seismic events of magnitude 7 and greater have occurred worldwide (EMSC) during the ten-year period. Several kinds of tilt anomalies were recognised within days up to months before the mainshocks. The most typical anomaly was a sudden tilting, parallel with the geologic structure, where the pendulum was installed. Based on the observations, we are proposing an asperity model, explaining the generation of so called “stress waves” before the mainshocks. Such stress waves of very low frequency (i.e. periods of days up to the first months) could be detected anywhere on the globe, especially on active geological structures, parallel with the fault, where a mainshock can happen. The observations suggest that we could estimate that part of the global fault system, which generates the detected stress wave, and which reaches the critical state. The estimation can be performed according to the amplitude of the stress wave, compared with stress waves detected on other structures of different orientations. According to the length of the stress wave (its period) and the tilt amplitude, it could be possible to estimate the magnitude of the mainshock.

Assessment of Adverse Engineering Geological Conditions during Seismic Microzonation of the Sentachan Mining and Refining Facility (Eastern Yakutia)

In this study, the authors used complex seismotectonic, geological and geophysical methods when carrying out scientific research, identifying unfavourable engineering geological conditions for the designed mining facility located in the cryolithozone, as well as when determining the level of basic seismic hazard and performing seismic microzonation. The seismotectonic methods consisted in establishing the relationship between the distribution of local earthquake epicentres and active geological structures. The geophysical studies employing the methods of near-surface seismic tomography and electrical resistivity tomography allowed obtaining of detailed and reliable information on the features of the engineering geological structure of the studied site required to assess the influence of soils on the seismic wave attenuation of possible earthquakes in the region, thus solving the issue of seismic microzonation.Seismotectonic studies consisted in determining the level of basic seismic hazard and were based mainly on previous field studies summarised in a number of published works, some of whose conclusions were used in this article.The analysis of geophysical data allowed the authors to establish probable location of the distributions of ice and ice-rich permafrost, as well as the heterogeneity of soil conditions that affect their behaviour under dynamic loads.The calculated values of probable earthquake intensities allowed the authors to determine the level of maximum earthquake intensity at the designed industrial sites of the mining and refining facility.

Occurrence of unconventional hydrocarbon deposits and its structural relation in Nepal Himalaya: implication for future exploration

Due to tectonic movement, compressed structures, and mountain upliftment process, several sedimentary basins have evolved in the periphery of the Himalayan orogeny. The evolution of sedimentary basins within the Central Himalaya (i.e., Nepal Himalaya) is quite similar in age (i.e., Eocene–Recent). The sedimentary sequences within this basin are marked by large-scale geological structures (e.g., Main Central Thrust, Main Boundary Thrust, and Main Frontal Thrust). The Lesser Himalayan (Eocene-Miocene) foreland basin in far western Nepal contains various hydrocarbon deposits. Similarly, the shallow marine shale, coal seams numerous fossils, and tight sand layers are the important sources of energy resources. The sedimentary basin, Surkhet Group in the western Nepal, is the prospective area for the unconventional hydrocarbon deposit. Due to active geological structures (such as Ranimatta Thrust, Budar Thrust, Mahabharat Thrust, and Nabi Khola Anticline), oil and gas seem to have migrated upward in the Padukasthan, Nabhisthan, and Sristhan. Therefore, the active oil and gas seepage occur locally in this area. Due to lack of scientific engineering research, the utilization of various energy resources of Central Himalaya (Nepal Himalaya) is important but challenging. There is not much work carried out on this section; the present study discussed about the relationship between the sedimentary structures and the formation of unconventional gas and its prospects in the Nepal Himalaya region.

Identification of geodynamic movements based on the results of geodetic monitoring measurements

The methodology and results of an experimental study of modern geodynamic movements using the data from geodetic deformation monitoring are presented. The related issues of modeling natural, anthropogenic, and ecological systems are considered. A technique for visualizing geodynamic movements based on the results of cyclic geodetic measurements, which allows to reasonably identify active geological structures, blocks, tectonic faults, is presented. It is shown that as a key source of information on geodynamic movements over large spatio-temporal intervals, it is advisable to use not the absolute values of the vectors of displacement of observation points, but their velocities, normalized to the annual cycle. It is indicated that an important characteristic of the vector field of geodynamic movements is divergence, which characterizes the degree of convergence or divergence of the vector flow.

Earthquake Risk Reduction Study with Mapping an Active Fault at the Southern of East Java

The southern part of Java Island is located between the two plates of the subduction zone, therefore this region had an active tectonic and volcanic activities. Those made a deformation of the geology around the southern part of Java island. This research was conducted to know the volume of deep geological structures to provide an overview of disaster warning systems in southern East Java region. The research that has been carried out using numerous active geophysical methods such as seismic methods had not been able to indicate internal structures. The needed for innovation used the integration of gravity and magnetotellurics methods. Bouguer anomaly gravity map became the supported data for interpretation. It showed low-density zones (0-80 mGal) between Pacitan-Trenggalek and beneath the Lumajang area which indicates the fault structure. Magnetotellurics (MT) which had a high penetration so that it is able to map deep active geological structures below the surface. The research area covered 8 regencies at the southern of East Java namely Pacitan, Trenggalek, Tulungagung, Blitar, Malang, Lumajang, Jember, and Banyuwangi. Magnetotelluric 1D processing showed indications of faults with orientations tend to be NE-SW between Pacitan and Trenggalek with depth (500 m – 8000 meter). Indications of faults with orientation tend to be NorthEast-SouthWest in Lumajang (100 - 500 meter).

Reevaluation of Active Geologic Structures in the Epicentral Area of the 2018 Northern Osaka Prefecture Earthquake Based on Geomorphological, Geological and Geophysical Exploration Data

Reevaluation of Active Geologic Structures in the Epicentral Area of the 2018 Northern Osaka Prefecture Earthquake Based on Geomorphological, Geological and Geophysical Exploration Data