Detection of repeating earthquakes in the West Bohemia swarm region

2020 ◽  
Author(s):  
Ali Salama ◽  
Tomas Fischer
Keyword(s):  
Fault Zone ◽  
Seismic Velocity ◽  
Background Activity ◽  
Source Parameters ◽  
The West ◽  
Data Set ◽  
Repeating Earthquakes ◽  
Waveform Cross Correlation ◽  
Cross Correlation Analysis ◽  
West Bohemia

<p> </p><p><span><strong> </strong></span></p><p> </p><p><span>Repeating earthquakes, sequences of microseismic events with highly similar seismograms and magnitudes, suggest quasi-periodic rupturing of the same asperity. They are observed on creeping fault segments surrounded by aseismic slip area and also in earthquake swarms. However, so far, they have not been documented in the West Bohemia/Vogtland seismic swarm area. These local swarms consist of thousands of M</span><sub><span>L</span></sub><span> < 4 events occurring along a small area of fault zone with repeated activation of some patches during the swarms and weak background activity in the intermediate periods. Detecting and analyzing the repeating earthquakes would help revealing the continuing background activity and identifying fault areas that are active permanently. This could point to the possible sources of fluids or aseismic creep that are supposed to play significant role in swarm generation. Repeating earthquakes are identified by waveform cross-correlation analysis comparing waveforms of repeaters with continuous seismic data set. We developed efficient detection algorithm to identify repeating earthquakes using selected event templates to reveal continuing seismic activity along the main Nový Kostel fault zone, namely in the areas with only episodic activity. The results provide a robust basis for routine application to the long-term seismic dataset that will allow also for further applications including analysis of the source parameters of the repeaters and/or detecting possible seismic velocity variations in the focal zone. </span></p><p> </p>

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>

Migration patterns of earthquake clusters

2020 ◽  
Author(s):  
Tomáš Fischer ◽  
Sebastian Hainzl
Keyword(s):  
Growth Velocity ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Hydraulic Fractures ◽  
Earthquake Physics ◽  
Data Set ◽  
Slow Slip Events ◽  
Migration Patterns ◽  
Pressure Diffusion ◽  
West Bohemia

<p>Earthquake hypocenter migration is the most characteristic pattern which indicates aseismic processes triggering the observed seismicity. These processes can involve creep, fluid migration or similar. While interactions among earthquakes can also lead to some expansion of seismic clouds, these expansions are rather small and not comparable to migration patterns related to pore-pressure diffusion, slow slip events, or growing hydraulic fractures. Thus, identification and modeling of migration patterns, which has not been studied in detail, is important for the characterization of fault dynamics.</p><p>Advance of the triggering front is usually analyzed using distance-time plots that show the time dependence of the distance of individual events from the origin. If event order is used instead of time as the argument on the horizontal axis, event migration is analyzed in dependence on the seismic activity itself, which brings a new view to the running seismicity. We applied this approach to the relocated earthquake swarm catalogs from West Bohemia, California and Iceland and found a striking linear growth of the triggering front. This indicates that the advance of the front is likely to be driven by the rupture of individual earthquakes rather than by the running time. It also turned out that the growth velocity measured in meters per event increases with the magnitude of the data set.</p><p>Using the basic concepts of earthquake physics, we propose the relation of the growth velocity on earthquake magnitudes and compare it with measurements on the analyzed swarm catalogues. We show that the spreading velocity of the triggering front is closely related to source parameters, which gives hints to the understanding of the background mechanism.</p>

First results from temporary deployment of small seismic network following the Mw=6.4 Petrinja earthquake

2021 ◽  
Author(s):  
Josip Stipčević ◽  
Valerio Poggi ◽  
Marijan Herak ◽  
Stefano Parolai ◽  
Davorka Herak ◽  
...  
Keyword(s):  
Fault Zone ◽  
Near Field ◽  
Source Parameters ◽  
Strong Motion ◽  
Aftershock Sequence ◽  
Seismic Network ◽  
Rupture Directivity ◽  
Data Set ◽  
First Results ◽  
Clustering Of Events

<p>The Department of Geophysics, University of Zagreb and the Italian National Institute of Oceanography and Applied Geophysics (OGS) installed on January 4th 2021, five temporary seismic stations near the town of Petrinja, Croatia, in the aftermath of  the 29 Decembre 2020 Mw 6.4 earthquake. The stations equipped with a seismometer and a strong motion sensor, recorded the aftershock sequence beginning six days after the mainshock allowing to augment the permanent seismic network in the area improving the azimuthal coverage and providing additional near‐field observations.</p><p>In this presentation we summarize the motivation and goals of the deployment; details regarding the station installation, instrumentation, and configurations and observations from the network. The collected data set will be useful for carrying out several seismological studies including the analysis of variability of strong ground motions in near field, the determination of the aftershocks source parameters,  the estimation (if any) of rupture directivity of small events, the clustering of events in space and time, the better imaging of the fault zone, the evolution of crustal properties within and outside of the fault zone.</p>

Constraints on the mantle transition zone structure using triplicated body waves

2021 ◽  
Author(s):  
Felix Bissig ◽  
Amir Khan ◽  
Domenico Giardini
Keyword(s):  
Transition Zone ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Body Wave ◽  
Source Parameters ◽  
Body Waves ◽  
Mantle Structure ◽  
Data Set ◽  
Mantle Transition Zone ◽  
Mantle Mineral

<p>The mantle transition zone (MTZ) is bounded by seismic discontinuities at average depths of 410 km and 660 km, which are generally associated with major mantle mineral transformations. A body wave impinging from above on these discontinuities develops a refracted and reflected branch, leading to multiple arrivals of the same wavetype within a short time window. These so-called triplicated body waves are observed at regional epicentral distances (15-30°) and carry information on MTZ structure due to their strong interaction with the 410 km and 660 km discontinuities. Careful data selection and processing as well as the assessment of source parameters are necessary steps in obtaining a high quality triplication data set. In this study, we consider recordings of events in Central America at permanent and transportable USArray stations, which are inverted for mantle structure. Our methodology is based on a joint consideration of mineral physics and seismic data in a probabilistic inversion framework and allows for determination of mantle thermo-chemical and seismic velocity structure. We present constraints on the mantle structure underneath the Gulf of Mexico.</p>

Cross-Correlation Analysis of Long-Term Ambient Seismic-Noise Recordings in the Caribbean Netherlands to Monitor the Volcanoes on Saba and St. Eustatius

2020 ◽  
Vol 110 (5) ◽  
pp. 2541-2558
Author(s):  
Reinoud Sleeman ◽  
Elske de Zeeuw-van Dalfsen
Keyword(s):  
Seismic Velocity ◽  
Sine Wave ◽  
Peak Ground Velocity ◽  
Data Set ◽  
Ground Shaking ◽  
Daily Monitoring ◽  
Cross Correlation Analysis ◽  
Single Station ◽  
Velocity Variations ◽  
Different Characteristics

ABSTRACT The continuous recordings of broadband seismometers on Saba and St. Eustatius in the Lesser Antilles provide a unique and long data set to measure temporal seismic velocity variations (dv/v) at two active but quiescent volcanoes (Mt. Scenery and The Quill). We compare results from single-station cross-component (SC) correlations with cross-station cross-component (CC) correlations and achieve the best similarities within the frequency band 1.3–2.1 Hz, with average correlations of 0.82 for Saba and 0.36 for St. Eustatius, justifying the use of SC as proxy for CC at these frequencies. Temporal dv/v variations derived from 13 yr of data show different characteristics at both islands. At St. Eustatius dv/v highly correlates (0.72) with air temperature and can be modeled by a simple sine wave with a period of 1 yr. Remaining residuals reveal cohurricane dv/v drops, thus at times of the passage of a hurricane. At Saba, subsurface velocity variations show temporal coseismic changes, up to −0.49% compared with −0.19% at St. Eustatius, and thus show a higher sensitivity to ground shaking. Our data set, although limited, shows a linear relation (correlation 0.78) between the coseismic dv/v drop and peak ground velocity at Saba around 1.3 Hz. We model the associated seismic velocity recovery with an exponential decay function and we estimate the recovery time at 2 yr. After subtracting the coseismic drop and recovery model, dv/v at Saba obtained from CC data correlates with the sine model (correlation 0.71). SC may be an appealing alternative for CC for monitoring purposes; however, the use of a small network is preferred to reduce the variance in dv/v (at St. Eustatius from 0.12% to 0.05%) and to detect dv/v variations unrelated to volcanic activity (e.g., hurricane). We continue work on the implementation of CC in the daily monitoring for Mt. Scenery and The Quill.

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.

scholarly journals Seismic velocity structure at the southern termination of the 2016 Kumamoto Earthquake rupture, Japan

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Yasuhira Aoyagi ◽  
Haruo Kimura ◽  
Kazuo Mizoguchi
Keyword(s):  
Fault Zone ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Earthquake Rupture ◽  
2016 Kumamoto Earthquake ◽  
Seismic Velocity Structure ◽  
Kumamoto Earthquake ◽  
Seismogenic Layer ◽  
The 2016 Kumamoto Earthquake ◽  
Tectonic Line

Abstract The earthquake rupture termination mechanism and size of the ruptured area are crucial parameters for earthquake magnitude estimations and seismic hazard assessments. The 2016 Mw 7.0 Kumamoto Earthquake, central Kyushu, Japan, ruptured a 34-km-long area along previously recognized active faults, eastern part of the Futagawa fault zone and northernmost part of the Hinagu fault zone. Many researchers have suggested that a magma chamber under Aso Volcano terminated the eastward rupture. However, the termination mechanism of the southward rupture has remained unclear. Here, we conduct a local seismic tomographic inversion using a dense temporary seismic network to detail the seismic velocity structure around the southern termination of the rupture. The compressional-wave velocity (Vp) results and compressional- to shear-wave velocity (Vp/Vs) structure indicate several E–W- and ENE–WSW-trending zonal anomalies in the upper to middle crust. These zonal anomalies may reflect regional geological structures that follow the same trends as the Oita–Kumamoto Tectonic Line and Usuki–Yatsushiro Tectonic Line. While the 2016 Kumamoto Earthquake rupture mainly propagated through a low-Vp/Vs area (1.62–1.74) along the Hinagu fault zone, the southern termination of the earthquake at the focal depth of the mainshock is adjacent to a 3-km-diameter high-Vp/Vs body. There is a rapid 5-km step in the depth of the seismogenic layer across the E–W-trending velocity boundary between the low- and high-Vp/Vs areas that corresponds well with the Rokkoku Tectonic Line; this geological boundary is the likely cause of the dislocation of the seismogenic layer because it is intruded by serpentinite veins. A possible factor in the southern rupture termination of the 2016 Kumamoto Earthquake is the existence of a high-Vp/Vs body in the direction of southern rupture propagation. The provided details of this inhomogeneous barrier, which are inferred from the seismic velocity structures, may improve future seismic hazard assessments for a complex fault system composed of multiple segments.

Sign in / Sign up

Export Citation Format

Share Document