scholarly journals Velocity structure and the role of fluids in the West Bohemia Seismic Zone

2014 ◽  
Vol 6 (1) ◽  
pp. 511-534
Author(s):  
C. Alexandrakis ◽  
M. Calò ◽  
F. Bouchaala ◽  
V. Vavryčuk
Keyword(s):  
Velocity Structure ◽  
Weighted Average ◽  
Tectonic Stress ◽  
Double Difference ◽  
Seismic Zone ◽  
The West ◽  
Fluid Concentration ◽  
West Bohemia ◽  
Basic Characteristics ◽  
Tomography Method

Abstract. In this study, we apply the double-difference tomography method to investigate the detailed 3-D structure within and around the Nový Kostel seismic zone, an area in the Czech Republic known for frequent occurrences of earthquake swarms. We use data from the extensively analyzed 2008 swarm, which has known focal mechanisms, principal faults, tectonic stress, source migration and other basic characteristics. We selected about 500 microearthquakes recorded at 22 local seismic stations of the West Bohemia Network (WEBNET). Applying double-difference tomography, combined with Weighted Average Model post-processing to correct for parameter dependence effects, we produce and interpret 3-D models of the Vp-to-Vs ratio (Vp/Vs) in and around the focal zone. The modeled Vp-to-Vs ratio shows several distinct structures, namely an area of high Vp-to-Vs ratio correlating with the microearthquakes, and a layer of low values directly above it. These structures may reflect changes in lithology and/or fluid concentration. The overlaying low Vp-to-Vs ratio layer coincides with high density metamorphic unit associated with the Fichtelgebirge (Smrčiny) granitic intrusion. It is possible that the base of the layer acts as a fluid trap, resulting in the observed periodic swarms.

scholarly journals Velocity structure and the role of fluids in the West Bohemia Seismic Zone

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 863-872 ◽  
Author(s):  
C. Alexandrakis ◽  
M. Calò ◽  
F. Bouchaala ◽  
V. Vavryčuk
Keyword(s):  
Velocity Structure ◽  
Weighted Average ◽  
Monitoring Network ◽  
Tectonic Stress ◽  
Double Difference ◽  
Seismic Zone ◽  
The West ◽  
Fluid Concentration ◽  
West Bohemia ◽  
Weighted Average Model

Abstract. In this study, we apply the double-difference tomography to investigate the detailed 3-D structure within and around the Nový Kostel Seismic Zone, an area in the Czech Republic known for frequent occurrences of earthquake swarms. We use data from the 2008 swarm since it has already been analysed in terms of earthquake focal mechanisms, principal faults, tectonic stress and foci migration. We selected about 500 microearthquakes recorded at 22 local seismic stations of the West Bohemia seismic monitoring network (WEBNET). Applying double-difference tomography, combined with weighted average model (WAM) post-processing to correct for parameter dependence effects, we produce and interpret 3-D models of the Vp-to-Vs ratio (Vp/Vs) in and around the focal zone. The modelled Vp/Vs ratio shows several distinct structures, namely an area of high Vp/Vs ratio correlating with the foci of the microearthquakes, and a layer of low values directly above it. These structures may reflect changes in lithology and/or fluid concentration. The overlaying low Vp/Vs ratio layer coincides with the base of the Fichtelgebirge (Smrčiny) granitic intrusion. It is possible that the base of the layer acts as a fluid trap and an upper limit to the seismicity, resulting in observed periodic swarms.

Improving the detection capability of the West Bohemian network by template matching approach 

2021 ◽  
Author(s):  
Ali Salama ◽  
Tomas Fischer
Keyword(s):  
Template Matching ◽  
Background Activity ◽  
Double Difference ◽  
The West ◽  
Data Set ◽  
S Waves ◽  
Repeating Earthquakes ◽  
Efficient Detection ◽  
West Bohemia ◽  
Manual Processing

<p><span>During the West-Bohemia/Vogtland earthquake swarms thousands of events are detected within short periods of few days, whose preliminary location is provided by an automated procedure. The manually verified high quality catalog is provided with some delay and is usually less complete than the automatic one. </span></p><p><span>We developed a template matching procedure combined with differential time measurement and double difference location whose application in real time will allow to provide precise hypocentre locations for much larger data set than provided by the manual processing. Among others, the template matching approach includes flexible setting of the time difference between P and S waves which allows for event detection in a wider distance to the template’s hypocentre. This makes the size of the template dataset small enough to allow for efficient detection process. </span></p><p><span>Our application of the template matching approach is aimed at identifying repeated activation of some patches during the swarms and weak background activity in the intermediate periods. Detecting and analyzing the repeating earthquakes will help revealing the continuing background activity and identifying fault areas that are active permanently. This will point to the possible sources of fluids or aseismic creep that are supposed to play significant role in swarm generation. </span></p>

Microseismic and Induced Seismicity Monitoring and Tomography of the Changning-Zhaotong shale gas play in China using dense nodal arrays

2020 ◽  
Author(s):  
Wen Yang ◽  
Junlun Li ◽  
Yuyang Tan ◽  
Yaxing Li ◽  
Jiawei Qian ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Velocity Structure ◽  
Double Difference ◽  
Steady Increase ◽  
S Wave ◽  
Two Phase ◽  
Arrival Times ◽  
Seismicity Monitoring ◽  
Tomography Method

<p>With the development of shale gas in the Changning-Zhaotong play in the southern Sichuan basin of China, which is the largest shale gas prospect in China, the frequency and magnitude of earthquakes in this region have increased significantly in recent years. For example, a M5.7 earthquake occurred on December 16, 2018, and a M5.3 earthquake on January 6, 2019 in addition to many M4.0+ earthquakes in this area. Some studies argue the large magnitude earthquakes are triggered by hydraulic fracturing in for the local shale gas development, which commenced in 2011. The frequency of the earthquake occurrence has been on steady increase in the past few years that local residents often reported felt quakes. To further understand the correlation between the shale gas development and local seismic activity, we conducted a two-phase dense array seismic monitoring with about 200 Zland 3C and SmartSolo 3C 5 Hz seismic nodes, from late February to early May, 2019 for a period of 70 days. The survey consists of roughly 340 deployments at 240 sites, with an average interstation distance of 1.5 km, covering 500 km<sup>2</sup> in total. We have processed seismic records from late February to early April, 2019 (phase I), and picked some 600,000 P- and S-wave arrival times from 4385 detected local earthquakes. The earthquake hypocenters and the subsurface velocity structure of the Changning-Zhaotong area are inverted for using the double-difference tomography method. The relocation results show that the majority of hypocenters were located at depths ranging from 1.0km to 4.0km, in the proximity of the horizontal hydraulic fracturing wells. The tomographic results (< 3 km) correlate well with the known surface geological units, and most earthquakes occurred along the velocity discontinuities, likely characterizing a large hidden fault which, interestingly, is where the January 2019 M5.3 occurred. Our study is very important for understanding the seismic potentials in this area, and should provide useful information for the shale gas development in this region and other areas in China with similar geological, tectonic and stress conditions.</p>

Marie Ulčová and her Contribution to the West Bohemian Museums

2018 ◽  
Vol 56 (1) ◽  
pp. 13-23
Author(s):  
Nela Štorková
Keyword(s):  
Twentieth Century ◽  
Second World War ◽  
World War ◽  
The West ◽  
West Bohemia ◽  
Long Time ◽  
Second World

While today the Ethnographic Museum of the Pilsen Region represents just one of the departments of the Museum of West Bohemia in Pilsen, at the beginning of the twentieth century, in 1915, it emerged as an independent institution devoted to a study of life in the Pilsen region. Ladislav Lábek, the founder and long-time director, bears the greatest credit for this museum. This study presents PhDr. Marie Ulčová, who joined the museum shortly after the Second World War and in 1963 replaced Mr. Lábek on his imaginary throne. The main objective of this article is to introduce the personality of Marie Ulčová and to evaluate the activity of this Pilsen ethnographer and the museum employee with an emphasis on her work in the Ethnographic Museum of the Pilsen Region. The basic aspects of the ethnographic activities, not only of Marie Ulčová but also of the Ethnographic Museum of the Pilsen Region in the years 1963–1988, are described through her professional and popularising articles, archival sources and contemporary periodicals.

Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area

2013 ◽  
Vol 118 (1) ◽  
pp. 120-137 ◽  
Author(s):  
Pavla Hrubcová ◽  
Václav Vavryčuk ◽  
Alena Boušková ◽  
Josef Horálek
Keyword(s):  
Moho Depth ◽  
The West ◽  
Depth Determination ◽  
West Bohemia

scholarly journals Structure-controlled asperities of the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes, NE Tibet, China, revealed by high-resolution seismic tomography

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Quan Sun ◽  
Shunping Pei ◽  
Zhongxiong Cui ◽  
Yongshun John Chen ◽  
Yanbing Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Tomography ◽  
High Velocity ◽  
Three Dimensional ◽  
Large Earthquake ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Double Difference ◽  
Source Regions ◽  
Large Earthquakes

AbstractDetailed crustal structure of large earthquake source regions is of great significance for understanding the earthquake generation mechanism. Numerous large earthquakes have occurred in the NE Tibetan Plateau, including the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes. In this paper, we obtained a high-resolution three-dimensional crustal velocity model around the source regions of these two large earthquakes using an improved double-difference seismic tomography method. High-velocity anomalies encompassing the seismogenic faults are observed to extend to depths of 15 km, suggesting the asperity (high-velocity area) plays an important role in the preparation process of large earthquakes. Asperities are strong in mechanical strength and could accumulate tectonic stress more easily in long frictional locking periods, large earthquakes are therefore prone to generate in these areas. If the close relationship between the aperity and high-velocity bodies is valid for most of the large earthquakes, it can be used to predict potential large earthquakes and estimate the seismogenic capability of faults in light of structure studies.

Rampart seismic zone of central Alaska

1983 ◽  
Vol 73 (3) ◽  
pp. 813-829
Author(s):  
P. Yi-Fa Huang ◽  
N. N. Biswas
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
B Value ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Lithospheric Plate ◽  
Normal Faults ◽  
Seismic Zone ◽  
The West ◽  
Fault Plane Solutions

abstract This paper describes the characteristics of the Rampart seismic zone by means of the aftershock sequence of the Rampart earthquake (ML = 6.8) which occurred in central Alaska on 29 October 1968. The magnitudes of the aftershocks ranged from about 1.6 to 4.4 which yielded a b value of 0.96 ± 0.09. The locations of the aftershocks outline a NNE-SSW trending aftershock zone about 50 km long which coincides with the offset of the Kaltag fault from the Victoria Creek fault. The rupture zone dips steeply (≈80°) to the west and extends from the surface to a depth of about 10 km. Fault plane solutions for a group of selected aftershocks, which occurred over a period of 22 days after the main shock, show simultaneous occurrences of strike-slip and normal faults. A comparison of the trends in seismicity between the neighboring areas shows that the Rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central Alaska. The seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression.

scholarly journals APPLICATION OF 3-D VELOCITY MODELS AND RAY TRACING IN DOUBLE DIFFERENCE EARTHQUAKE LOCATION ALGORITHMS: APPLICATION TO THE MYGDONIA BASIN (NORTHERN GREECE)

2004 ◽  
Vol 36 (3) ◽  
pp. 1396 ◽  
Author(s):  
O. C. Galanis ◽  
C. B. Papazachos ◽  
P. M. Hatzidimitriou ◽  
E. M. Scordilis
Keyword(s):  
Ray Tracing ◽  
Velocity Structure ◽  
Test Site ◽  
Earthquake Location ◽  
Double Difference ◽  
Northern Greece ◽  
Local Networks ◽  
Velocity Models ◽  
Earthquake Locations

In the past years there has been a growing demand for precise earthquake locations for seismotectonic and seismic hazard studies. Recently this has become possible because of the development of sophisticated location algorithms, as well as hardware resources. This is expected to lead to a better insight of seismicity in the near future. A well-known technique, which has been recently used for relocating earthquake data sets is the double difference algorithm. In its original implementation it makes use of a one-dimensional ray tracing routine to calculate seismic wave travel times. We have modified the implementation of the algorithm by incorporating a three-dimensional velocity model and ray tracing in order to relocate a set of earthquakes in the area of the Mygdonia Basin (Northern Greece). This area is covered by a permanent regional network and occasionally by temporary local networks. The velocity structure is very well known, as the Mygdonia Basin has been used as an international test site for seismological studies since 1993, which makes it an appropriate location for evaluating earthquake location algorithms, with the quality of the results depending only on the quality of the data and the algorithm itself. The new earthquake locations reveal details of the area's seismotectonic structure, which are blurred, if not misleading, when resolved by standard (routine) location algorithms.

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