scholarly journals Relationship between seismicity and active faults in Thanh Hoa province detected by local seismic network

2021 ◽  
Vol 43 (2) ◽  
pp. 199-219
Author(s):  
Duong T. N. ◽  
Lai Hop Phong ◽  
Pham D. N. ◽  
Chen C. H. ◽  
Dinh V. T.
Keyword(s):  
Seismic Activity ◽  
Active Faults ◽  
Seismic Network ◽  
Local Network ◽  
Ground Acceleration ◽  
Magnetotelluric Data ◽  
Seismogenic Source ◽  
Tectonically Active ◽  
Relationship Of ◽  
The Relationship

Thanh Hoa province belongs to the southwest part of Northwest Vietnam, which is considered a tectonically active region. In the area of Thanh Hoa province, there are three deep-seated tectonic faults, namely Son La-Bim Son, Song Ma, and Sop Cop. As predicted by scientists, these faults are capable of producing credible earthquakes that might be the strongest in the territory of Vietnam. Besides the three main seismogenic sources, in the province, there are other smaller active faults such as Thuong Xuan-Ba Thuoc and Thuong Xuan-Vinh Loc but the relationship of these faults with seismic activity is still rather blurred. This may due to the sparseness of the Vietnamese National Seismic Network which can not record adequately small earthquakes in the area. This paper presents new results of additional monitoring from a local seismic network using 12 Guralp - 6TD broadband seismometers that have been deployed in Thanh Hoa province since November 2009. We found that the Thanh Hoa area is not seismically quiet. The average number of earthquakes recorded by the network has reached 80 - 90 events per year and some of them have magnitude from ML 3.0 to 4.0.By integration of the earthquake epicenters derived from the local network and distribution of active faults, we can detect several earthquakes locating near the three active faults, not only along the main faults but also along its subsidiary faults. We focused on the active faults of Thuong Xuan-Ba Thuoc and Thuong Xuan-Vinh Loc by using the recent results of the gravity, seismic, and magnetotelluric data analyses. Several recorded earthquakes distribute along the two small faults and some of them reach magnitude 3.0 or greater on the ML scale. In this study, the Thuong Xuan-Vinh Loc is recognized as a seismogenic source. To identify seismic hazard potential caused by earthquakes generated from the active faults, segmentation of the Thuong Xuan - Ba Thuoc fault had been done based on geological and geomorphological indications and seismic activity, and then the peak ground acceleration was determined for each fault segment. Besides, a large number of earthquake epicenters do not have a good correlation with a specific fault, especially in the area of Thanh Hoa coastal plain, which is covered by thick layers of Neogene - Quaternary sediment. This shows that there may be hidden active faults in the area which are needed to study further.

scholarly journals Relationship between seismicity and active faults in Thanh Hoa province detected by local seismic network

2021 ◽  
Vol 43 (2) ◽  
Author(s):  
Duong T. N. ◽  
Lai Hop Phong ◽  
Pham D. N. ◽  
Chen C. H. ◽  
Dinh V. T.
Keyword(s):  
Seismic Activity ◽  
Active Faults ◽  
Seismic Network ◽  
Local Network ◽  
Ground Acceleration ◽  
Magnetotelluric Data ◽  
Seismogenic Source ◽  
Tectonically Active ◽  
Relationship Of ◽  
The Relationship

Thanh Hoa province belongs to the southwest part of Northwest Vietnam, which is considered a tectonically active region. In the area of Thanh Hoa province, there are three deep-seated tectonic faults, namely Son La-Bim Son, Song Ma, and Sop Cop. As predicted by scientists, these faults are capable of producing credible earthquakes that might be the strongest in the territory of Vietnam. Besides the three main seismogenic sources, in the province, there are other smaller active faults such as Thuong Xuan-Ba Thuoc and Thuong Xuan-Vinh Loc but the relationship of these faults with seismic activity is still rather blurred. This may due to the sparseness of the Vietnamese National Seismic Network which can not record adequately small earthquakes in the area. This paper presents new results of additional monitoring from a local seismic network using 12 Guralp - 6TD broadband seismometers that have been deployed in Thanh Hoa province since November 2009. We found that the Thanh Hoa area is not seismically quiet. The average number of earthquakes recorded by the network has reached 80 - 90 events per year and some of them have magnitude from ML 3.0 to 4.0.By integration of the earthquake epicenters derived from the local network and distribution of active faults, we can detect several earthquakes locating near the three active faults, not only along the main faults but also along its subsidiary faults. We focused on the active faults of Thuong Xuan-Ba Thuoc and Thuong Xuan-Vinh Loc by using the recent results of the gravity, seismic, and magnetotelluric data analyses. Several recorded earthquakes distribute along the two small faults and some of them reach magnitude 3.0 or greater on the ML scale. In this study, the Thuong Xuan-Vinh Loc is recognized as a seismogenic source. To identify seismic hazard potential caused by earthquakes generated from the active faults, segmentation of the Thuong Xuan - Ba Thuoc fault had been done based on geological and geomorphological indications and seismic activity, and then the peak ground acceleration was determined for each fault segment. Besides, a large number of earthquake epicenters do not have a good correlation with a specific fault, especially in the area of Thanh Hoa coastal plain, which is covered by thick layers of Neogene - Quaternary sediment. This shows that there may be hidden active faults in the area which are needed to study further.

scholarly journals FEATURES OF DISTRIBUTION OF SEISMIC ACTIVITY IN DIFFERENT REGIONS OF EARTH OVER PHASES OF THE 11-YEAR SOLAR CYCLE

2020 ◽  
Vol 6 (1) ◽  
pp. 93-101
Author(s):  
Valeriy Ruzhich ◽  
Elena Levina
Keyword(s):  
Solar Cycle ◽  
Seismic Activity ◽  
Time Parameter ◽  
Superposition Method ◽  
Medium Term ◽  
Activity Distribution ◽  
Middle Latitudes ◽  
Northern Regions ◽  
Relationship Of ◽  
The Relationship

We discuss the relationship of solar activity with the seismicity of Earth and reasons for the differences in the results of studies of various authors. Using the epoch superposition method, we analyze the differences in seismic activity distribution over phases of the 11-year solar cycle for the whole world, hemispheres, sectors, latitudinal belts, and individual regions. The northeastern sector of Earth has been shown to make the main contribution to the planetary distribution of seismic activity over phases of the 11-year solar cycle. We have revealed a pattern in the distribution of seismic activity over latitudinal belts: the solar cycle phases, at which the main maximum of seismic activity occurs, increase with increasing latitude in both hemispheres. For some regions, the results may differ from the generalized results for Earth due to the influence of local geodynamic conditions during the destruction of the earth's crust. In middle latitudes, the maximum number of earthquakes is shifted to the later phases of the solar cycle from west to east, which was not found for the northern regions. We discuss possible reasons for various manifestations of solar-terrestrial relationships for different regions, taking into account their different structure and geodynamic development modes. The presence of pronounced maxima of the seismic activity distribution over the 11-year solar cycle phases allows us to use them for refining the “time” parameter in the medium-term prediction of dangerous earthquakes.

scholarly journals Analysis of relationships among coastal alluvial fans and their contributing catchments in North Evoikos Gulf (Central Greece).

2016 ◽  
Vol 47 (1) ◽  
pp. 344 ◽  
Author(s):  
K. Valkanou ◽  
E. Karymbalis ◽  
D. Papanastassiou ◽  
K. Gaki-Papanastassiou ◽  
P. Giles
Keyword(s):  
Debris Flow ◽  
East Coast ◽  
Drainage Basin ◽  
Active Faults ◽  
Alluvial Fans ◽  
Drainage Basins ◽  
Central Greece ◽  
Depositional Processes ◽  
Tectonically Active ◽  
The Relationship

This paper deals with the morphometric analysis of 42, late Holocene, coastal alluvial fans located along the coasts of the tectonically active North Evoikos Gulf in central Greece. Thirty six of the fans have been formed by streams that discharge along the east coast of the Gulf (Evia Island) while the rest are located on the opposite side (Continental Greece). Selected morphometric parameters of the drainage basins were measured using topographic maps at the scale of 1:50,000 while those of the fans were derived from detailed topographic diagrams at the scale of 1:5,000 utilizing ESRI’s ArcGIS9.3 software. Fans were classified into four groups according to the primary depositional processes (fluvial and/or debris flow). Another classification criterion was the relationship between the location of the fan-catchment system and the local tectonic patterns (active faults). Fan-basin morphometric relationships for each fan group were also investigated. A strong positive relation was found between the size of the fan and the drainage basin area while the correlation between drainage area and fan slope was negative. Large catchments located near fault terminations have formed gently sloping fans dominated by fluvial processes, whereas torrents with small rough drainage basins, developed on the footwall, have formed steep fans likely dominated by debris-flow along the east coast of the Gulf

scholarly journals FEATURES OF DISTRIBUTION OF SEISMIC ACTIVITY IN DIFFERENT REGIONS OF EARTH OVER PHASES OF THE 11-YEAR SOLAR CYCLE

2020 ◽  
Vol 6 (1) ◽  
pp. 116-125
Author(s):  
Valeriy Ruzhich ◽  
Elena Levina
Keyword(s):  
Solar Cycle ◽  
Seismic Activity ◽  
Time Parameter ◽  
Superposition Method ◽  
Medium Term ◽  
Activity Distribution ◽  
Middle Latitudes ◽  
Northern Regions ◽  
Relationship Of ◽  
The Relationship

We discuss the relationship of solar activity with the seismicity of Earth and reasons for the differences in the results of studies of various authors. Using the epoch superposition method, we analyze the differences in seismic activity distribution over phases of the 11-year solar cycle for the whole world, hemispheres, sectors, latitudinal belts, and individual regions. The northeastern sector of Earth has been shown to make the main contribution to the planetary distribution of seismic activity over phases of the 11-year solar cycle. We have revealed a pattern in the distribution of seismic activity over latitudinal belts: the solar cycle phases, at which the main maximum of seismic activity occurs, increase with increasing latitude in both hemispheres. For some regions, the results may differ from the generalized results for Earth due to the influence of local geodynamic conditions during the destruction of the earth's crust. In middle latitudes, the maximum number of earthquakes is shifted to the later phases of the solar cycle from west to east, which was not found for the northern regions. We discuss possible reasons for various manifestations of solar-terrestrial relationships for different regions, taking into account their different structure and geodynamic development modes. The presence of pronounced maxima of the seismic activity distribution over the 11-year solar cycle phases allows us to use them for refining the “time” parameter in the medium-term prediction of dangerous earthquakes.

Earthquake-induced Transient Ground Strains from Dense Seismic Networks

2008 ◽  
Vol 24 (2) ◽  
pp. 453-470 ◽  
Author(s):  
Roberto Paolucci ◽  
Chiara Smerzini
Keyword(s):  
Spatial Interpolation ◽  
Strain Tensor ◽  
Ground Surface ◽  
Numerical Differentiation ◽  
Engineering Practice ◽  
Ground Acceleration ◽  
Wave Passage ◽  
Seismic Networks ◽  
Relationship Of ◽  
The Relationship

Earthquake-induced transient ground strains are evaluated based on the records obtained by two dense seismic networks, namely the Parkway Valley, New Zealand, and the UPSAR, California, arrays. The calculations are based on the spatial interpolation of the recorded displacements and a numerical differentiation to obtain the strain tensor at ground surface. The computed peak ground strains show an important dependence on azimuth, by a factor of about two. Furthermore, the relationship of the peak ground strains as a function of the most common measures of ground motion severity, such as peak ground acceleration, velocity and displacement, is explored. Our results are in reasonable agreement with other published relationships and with some of the few available direct records of strain. However, they point out the limitations of the simplified evaluations used in the engineering practice, which uniquely consider the wave passage effect on the ground strain evaluation, and tend to significantly underestimate the observations.

scholarly journals Integrating faults and past earthquakes into a probabilistic seismic hazard model for peninsular Italy

2017 ◽  
Author(s):  
Alessandro Valentini ◽  
Francesco Visini ◽  
Bruno Pace
Keyword(s):  
Seismic Hazard ◽  
Seismic Activity ◽  
Active Faults ◽  
Gaussian Model ◽  
Probabilistic Seismic Hazard ◽  
Maximum Magnitude ◽  
Ground Acceleration ◽  
Slip Rates ◽  
Earthquake Sources ◽  
The Impact

Abstract. Italy is one of the most seismically active countries in Europe. Moderate to strong earthquakes, with magnitudes of up to ~ 7, have been recorded on many of active faults in historical times. Currently, probabilistic seismic hazard assessments in Italy are mainly based on area source models, in which the seismicity is modelled on a number of seismotectonic zones and the occurrence of earthquakes is assumed to be uniform. However, in the last decade, efforts have increasingly been directed towards using fault sources in seismic hazard models to obtain more detailed and possibly more realistic patterns of ground motion. In our model, we used two categories of earthquake sources. The first involves active faults, and fault slip rates were used to quantify the seismic activity rate. We produced an inventory of all fault sources, with details on their geometric, kinematic and energetic properties. The parameters are used to compute the total seismic moment rate for each fault. We evaluated the magnitude-frequency distributions of each fault source using two models, a characteristic Gaussian model centred on the maximum magnitude and a Truncated Gutenberg-Richter model. The second earthquake source category involves distributed seismicity, and a fixed-radius smoothed approach and a historical catalogue were used to evaluate seismic activity. Under the assumption that deformation is concentrated along faults, we combined the earthquakes derived from the geometry and slip rates of active faults with the earthquakes from the spatially smoothed earthquake sources and assumed that the smoothed seismic activity in the vicinity of an active fault gradually decreases by a fault-size driven factor. We computed horizontal peak ground acceleration maps for return periods of 475 and 2,475 yr. Although the range and gross spatial distribution of the expected accelerations obtained here are comparable to those obtained through methods involving seismic catalogues and classical zonation models, the spatial pattern of our model is far more detailed. Our model is characterized by areas that are more hazardous and that correspond to mapped active faults, while the previous models yield expected accelerations that are almost uniformly distributed across large regions. In addition, we conducted sensitivity tests to determine the impact on the hazard results of the earthquake rates derived from two magnitude-frequency distribution models for faults and to determine the relative contributions of faults versus distributed seismic activity. We think our model represents an advance for Italy in terms of input data (quantity and quality) and methodology in the field of the fault-based regional seismic hazard modelling.

The Mt. Rainier earthquake of July 18, 1973, and its tectonic significance

1975 ◽  
Vol 65 (2) ◽  
pp. 393-401 ◽  
Author(s):  
Robert S. Crosson ◽  
David Frank
Keyword(s):  
Puget Sound ◽  
Active Faults ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Aerial Photographs ◽  
Tectonic Significance ◽  
Earthquake Generation ◽  
Surrounding Areas ◽  
Relationship Of ◽  
The Relationship

abstract On July 18, 1973, a magnitude 3.9 earthquake was strongly felt at Longmire and surrounding areas near Mt. Rainier, Washington. Network analysis permitted an accurate hypocenter to be located at 46°49.29′N and 121°49.86′W at a depth of 10.9 km, about 7 km southwest of the summit of Mt. Rainier. No prolonged aftershock sequence was generated, although two small aftershocks were recorded and located. Aerial photographs of the epicentral region reveal several northwest-trending lineaments which may be related to active faults in the region, although no surface ground breakage was discovered. The focal mechanism obtained for the main shock is well constrained and consistent with right-lateral strike-slip motion along a northwest-trending fracture, in general agreement with northwest-trending surface lineaments. The nature of the relationship of the earthquake occurrence to Mt. Rainier is uncertain. The principal compressive axis direction is in agreement with that found in the central Puget Sound basin. However, the shallow depths, the strike-slip mode of faulting, and the past evidence of earthquakes near Mt. Rainier suggest a direct relationship between faulting, earthquake generation, and the volcano location.

The relationship of the scleractinian corals to the rugose corals

Paleobiology ◽  
1980 ◽  
Vol 6 (02) ◽  
pp. 146-160 ◽  
Author(s):  
William A. Oliver
Keyword(s):  
Critical Points ◽  
Scleractinian Corals ◽  
Convincing Evidence ◽  
Early Triassic ◽  
Rugose Corals ◽  
History Of ◽  
The Subject ◽  
Relationship Of ◽  
The Relationship ◽  
Biologic Factors

The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.

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