Automatic monitoring of crustal seismic activity in Galati region of southeastern Romania using full waveform-based approach

2020 ◽  
Author(s):  
Dragos Tataru ◽  
Natalia Poiata ◽  
Bogdan Grecu
Keyword(s):  
Seismic Activity ◽  
Velocity Structure ◽  
Automatic Monitoring ◽  
Seismic Monitoring ◽  
Local Network ◽  
Earthquake Catalog ◽  
Small Magnitude ◽  
Seismic Swarm ◽  
Full Waveform ◽  
Shallow Velocity Structure

<p>In September–November 2013 a seismic swarm occurred in Galati region of southeastern Romania. The area was previously known as characterized by low seismic activity along the major crustal faults. During the period of swarm, between September 23rd and November 5<sup>th</sup>, over 1000 events with the magnitudes (Ml) of 0.2–4.0, located at the depth of 5–10 km, have been detected. Despite the relatively small magnitude, events generated ground motions that were well felt by local people, leading to panic in the area. The proximity of active oil fields caused additional annoyance.</p><p>Advanced seismic monitoring in the region started in 2013 with deployment of mobile seismic stations immediately after the beginning of the swarm. Additionally, active seismic measurements were performed in order to characterize the shallow velocity structure at specific sites. Starting from July 2015 new permanents stations were installed in the area marking the beginning of Galati local network development. The routine seismic catalog derived using the acquired data and applying the standard detection and location techniques pointed that area continues to be seismically active, however with low rate of activity and magnitude of events. These made it a perfect study case for development of new advanced schemes for seismic monitoring of the regions with low and complex seismicity aiming on an understanding of the phenomenon underlying the 2013 seismic swarm as well as the current seismic activity in the area.</p><p>We developed and automatic monitoring scheme based on the network-based full waveform detection and location method BackTrackBB (Poiata et al. 2016) that exploits the coherency of signals’ statistical features recorded across the seismic network. Once extracted from the flux of continuous data, seismic events are compared against the database of previously detected events using coherency and allowing to identify potential repeaters or multiplets. The earthquake catalog provided by the system starting from 2017 was compared to the routine ROMPLUS catalog of NIEP showing an increase in the number of detected events by the order of 3. We present the details of the implementation and discuss its advantages and drawbacks.</p>

scholarly journals Background seismicity and seismic monitoring in the Lai Chau reservoir area

2019 ◽  
Vol 23 (6) ◽  
pp. 1373-1390
Author(s):  
Grzegorz Lizurek ◽  
Jan Wiszniowski ◽  
N. V. Giang ◽  
D. Q. Van ◽  
L. V. Dung ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Moment Tensor ◽  
Synthetic Data ◽  
Seismic Monitoring ◽  
Local Network ◽  
Regional Seismicity ◽  
Seismic Catalogue ◽  
Reservoir Impoundment ◽  
The Future ◽  
Passive Seismic

Abstract Reservoir-triggered seismic activity depends not only on the technical characteristics of the future reservoir (filling volume, the height of water column) but also on the seismo-tectonics and the natural seismic processes occurring in the area before construction of an artificial reservoir. Passive seismic monitoring was realised near Lai Chau (Vietnam) before the impoundment started. It allowed exploration of the natural seismicity in the area of the future dam. Locations of seismic events several months prior to the reservoir impoundment were observed with ten stations installed in the reservoir vicinity. Events were mainly located near the dam along the Da river headwaters fault. However, only four stations were available for the entire period before the impoundment. Despite the network limitations, completeness of seismic catalogue and b value were determined and may be used as a baseline for analysis of the seismicity in this area after impoundment. The magnitude completeness level is significantly smaller than in the broader seismogenic zones covering an area of the dam. The b value differs from the results obtained for regional seismicity of Northeastern Vietnam. The capability of the local network for moment tensor inversion was estimated with the use of synthetic data tests. Test results provided the requirements for the station number according to azimuthal coverage of the network to obtain the reliable full moment tensor (MT) solution. Preliminary analysis of the seismic activity after Lai Chau reservoir impoundment indicates some changes in activity related to the impoundment and reservoir exploitation.

Basic principles for building seismic monitoring systems in rockburst-hazardous coal seam mining

2021 ◽  
pp. 8-12
Author(s):  
E. E. Razumov ◽  
◽  
S. M. Prostov ◽  
G. D. Rukavishnikov ◽  
S. N. Mulev ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Average Energy ◽  
Seismic Monitoring ◽  
Acoustic Properties ◽  
Signal Frequency ◽  
Monitoring Systems ◽  
Seismic Events ◽  
Seismic Monitoring Systems ◽  
Seismic Sensors ◽  
Seam Mining

The main directions of development of seismic monitoring systems in underground mineral mining are analyzed. The expediency of passive registration of natural seismic activity is proved, which provides prediction of geodynamic phenomena by locating the centers of seismic events and determining their energy level. The methods of active seismic monitoring (seismic tomography, cross-borehole survey, recording of seismic signal from a rock-breaking tool) are technically more difficult to implement. The promising methods for processing seismic information are geolocation, neural network technology, cluster analysis, and integration with numerical stress–strain analysis of and changes in acoustic properties of rock mass. The configuration of the platform developed at VNIMI and the GITS seismic monitoring system, which includes from 6 to 12 three-component seismic sensors installed permanently in wells or on pedestals, is described. The detailed layouts of seismic sensors at recording points and in gateways in extraction panels are presented. The main technical characteristics of GITS are given: the signal frequency range is 0.1–1000 Hz, the minimum recorded signal level is 0.01 mV. The main test data of GITS in Komsomolskaya mine of Vorkutaugol are described: the average annual levels of seismic activity and energy of seismic events are found to be relatively stable; the relationship between seismic event with the maximum total energy and the alternating increment in the relative criterion is defined, and the local increase in the average energy of a single event in time from the moment the main roof caving is identified. Aimed to substantiate the regional and local prediction criteria of probability of geodynamic events caused by confining pressure, VNIMI implements integrated research in mines in different regions.

NEW APPROACHES TO THE SYNTHESIS OF AUTOMATIC SEISMIC MONITORING SYSTEMS

2020 ◽  
pp. 73-81
Author(s):  
B. M. Shubik ◽  
Keyword(s):  
Monitoring System ◽  
Traditional Approach ◽  
Automatic Monitoring ◽  
Seismic Monitoring ◽  
Monitoring Systems ◽  
Computational Techniques ◽  
Frequency Model ◽  
Complexity Of Algorithms ◽  
New Approaches ◽  
Detection And Localization

The processes of development of hydrocarbon deposits are accompanied, as a rule, by an increase in the level of seismicity and, in particular, by the occurrence of technogenic earthquakes and other deformation phenomena associated with changes in the geodynamic regime. To monitor deformation and geodynamic processes, a seismic monitoring service should be organized. A similar monitoring system is also required for the analysis of aftershock and volcanic activity. Monitoring technology should be based on the use of reliable and fast methods of automatic detection and localization of seismic events of various scales. Traditional approaches to the detection and localization of earthquake epicenters and hypocenters are based on the analysis of data recorded by one or more single seismic stations. In that case, seismic event coordinates are estimated by means of signal extraction from noise and accurately measuring arrival times of a number of specific phases of the seismic signal at each recording point. Existing computational techniques have inherited this traditional approach. However, automatic procedures based on the ideology of manual processing turn out to be extremely laborious and ineffective due to the complexity of algorithms adequate to the actions of an experienced geophysicist-interpreter. The article contains a description of new approaches to the synthesis of automatic monitoring systems, which are based on the principles of emission tomography, use of spatial registration systems, energy analysis of wave fields and methods of converting real waveforms into low-frequency model signals (so-called filter masks/templates). The monitoring system was successfully tested in the process of detecting and locating the epicenters and hypocenters of 19 weak local earthquakes in Israel, as well as a quarry explosion.

scholarly journals A generic model for the shallow velocity structure of volcanoes

2018 ◽  
Vol 356 ◽  
pp. 114-126 ◽  
Author(s):  
Philippe Lesage ◽  
Michael J. Heap ◽  
Alexandra Kushnir
Keyword(s):  
Velocity Structure ◽  
Generic Model ◽  
Shallow Velocity Structure

New insights into structure and seismicity of the Central Alps from 3D Pg and Sg tomography and improved hypocenter relocations

2021 ◽  
Author(s):  
Tobias Diehl ◽  
Edi Kissling ◽  
Marco Herwegh ◽  
Stefan Schmid
Keyword(s):  
Velocity Structure ◽  
Focal Depth ◽  
Small Scale ◽  
Earthquake Catalog ◽  
Depth Range ◽  
Central Alps ◽  
Quartz Content ◽  
Phase Selection ◽  
Velocity Inversion ◽  
Velocity Models

<p>Accuracy of hypocenter location, in particular focal depth, is a precondition for high-resolution seismotectonic analysis of natural and induced seismicity. For instance, linking seismicity with mapped fault segments requires hypocenter accuracy at the sub-kilometer scale. In this study, we demonstrate that inaccurate velocity models and improper phase selection can bias absolute hypocenter locations and location uncertainties, resulting in errors larger than the targeted accuracy. To avoid such bias in densely instrumented seismic networks, we propose a coupled hypocenter-velocity inversion restricted to direct, upper-crustal Pg and Sg phases. The derived three-dimensional velocity models, combined with dynamic phase selection and non-linear location algorithms result in a highly accurate earthquake catalog, including consistent hypocenter uncertainties. We apply this procedure to about 60’000 Pg and 30’000 Sg quality-checked phases of local earthquakes in the Central Alps region. The derived tomographic models image the Vp and Vs velocity structure of the Central Alps’ upper crust at unprecedented resolution, including small-scale anomalies such as those caused by a Permo-Carboniferous trough in the northern foreland, Subalpine Molasse below the Alpine front or crystalline basement units within the Penninic nappes. The external Aar Massif is characterized by low Vp/Vs ratios of about 1.625-1.675 in the depth range of 2-6.5 km, which we relate to a felsic composition of the uplifted crustal block, possibly with increased quartz content. Finally, we discuss along-strike variations imaged by relocated seismicity in the Central Alps and demonstrate how joint interpretation of velocity structure and hypocenters provides additional constraints on lithologies of upper-crustal seismicity.</p>

Seismic Hazard Estimation in East China Offshore Areas

2013 ◽  
Vol 690-693 ◽  
pp. 1158-1167
Author(s):  
Li Fang Zhang ◽  
Yan Ju Peng ◽  
Zhen Ming Wang
Keyword(s):  
Seismic Hazard ◽  
Seismic Activity ◽  
Hazard Analysis ◽  
Seismic Hazard Analysis ◽  
East China ◽  
Earthquake Catalog ◽  
Ground Acceleration ◽  
Study Region ◽  
Seismicity Model ◽  
Seismic Hazard Estimation

In this study, we chose East China offshore areas as study region(N25°~41°，E117°~126°).According to the tectonic environments and characteristics of earthquake the seismotectonic units were established, taking Gaussian spatially smoothing only based on the input earthquake catalog, and fault-rupture-oriented elliptical smoothing to calculate the seismic activity rate in each cells. The maps for the distribution of horizontal peak ground acceleration with 10% probability of exceedance in 50 years were obtained through using the method of seismic hazard analysis based on cell source. While the total number of earthquakes unchanged, two-stage smoothing procedure deals with the error of epicenter location, contains the seismotectonic information in elliptical smoothing seismicity model. This method build up a simple and easy methodology of probabilistic seismic hazard analysis, especially for those place where not yet been clearly master the seismic tectonic information and with distributed Seismic activity.

Sign in / Sign up

Export Citation Format

Share Document