Analysis of the Seismic Activity in the Vrancea Intermediate-Depth Source Region During the Period 2010–2015

2016 ◽  
pp. 189-203 ◽  
Author(s):  
Andreea Craiu ◽  
Mihail Diaconescu ◽  
Marius Craiu ◽  
Alexandru Marmureanu ◽  
Constantin Ionescu
Keyword(s):  
Seismic Activity ◽  
Source Region ◽  
Intermediate Depth

Imaging the source region of Cascadia tremor and intermediate-depth earthquakes

Geology ◽  
2009 ◽  
Vol 37 (12) ◽  
pp. 1119-1122 ◽  
Author(s):  
G. A. Abers ◽  
L. S. MacKenzie ◽  
S. Rondenay ◽  
Z. Zhang ◽  
A. G. Wech ◽  
...  
Keyword(s):  
Source Region ◽  
Intermediate Depth

The Waveform Characteristics and Classification of Intermediate-depth Earthquakes in Ryukyu Subduction Zone

2020 ◽  
Author(s):  
Yu-Jhen Lin ◽  
Tai-Lin Tseng ◽  
Wen-Tzong Liang
Keyword(s):  
Subduction Zone ◽  
High Frequency ◽  
Time Window ◽  
Source Region ◽  
Focal Depth ◽  
Low Frequency ◽  
Frequency Content ◽  
Low Velocity ◽  
Waveform Data ◽  
Intermediate Depth

<p>Using intraslab earthquakes shallower than 150 km in the southernmost Ryukyu subduction zone, previous studies in Taiwan found the wave guide effect that typically shows a low-frequency (<2Hz) first P arrival followed by sustained high-frequency (3–10 Hz) wave trains. Recently occurred deeper events at depth 150-300 km allow us to better quantify the properties of those seismic waves traveling in the subduction zone. In this study, we aim to systematically scan through the local broadband waveforms of the intermediate depth earthquakes with M>5 between 1997 and 2016. Event are classified based on the waveform characteristics and their frequency contents.</p><p>To detect events with similar properties, we applied sliding-window cross-correlation (SCC)​ using three components of P waveform data simultaneously for a set of stations​. The time window used here was 10 s and traces were bandpass filtered in the frequency range 0.5–10 Hz. After the degree of similarity are calculated, e​vents containing comparable waveforms can be sorted into families. The events within a family would have been triggered because they came from the same source region and their paths to a particular receiver should produce similar waveforms. Our results show that most earthquakes are low in waveform similarity, implying no “repeating” behavior for those intermediate intraslab events. However, some events (cc>0.6 threshold) present enough charterers that can be grouped as a family.</p><p>One important property is the frequency content of the arrivals that may be related to the speed of structure traveled. We have developed a work scheme to determine the delayed time of higher-frequency energy. On family of events show beautiful dispersion with arrival time smoothly increasing with frequency between 0.5 and 6 Hz.​ Another type of dispersive waveforms appear as two distinct arrivals: low frequency and then high-frequency energy, separated by around 1 s. The time delay seems to be independent of focal depth. The latter case has been reported in the previous study for shallower event and it was interpreted as effect from low-velocity layer or heterogeneity of the subducted slab. On the other hand, the continuous dispersion is a new feature observed by our study, which may infer a thinner layer and/or longer propagation for some kind of reflecting waves to develop such interference.</p><p>In addition, we will classify the waveforms according to the frequency content and decay of coda. The variations in P coda properties can be associated with the way in which the seismic energy gets ducted into the stochastic waveguide associated with the lithosphere. With sufficient amount of data, it is possible to further identify the earthquakes with unusual source properties or structure anomaly along specific propagation paths. We expect the classification results can provide a reference for future numerical simulation analysis. </p><p>Keywords: Ryukyu subduction zone, SCC, guide wave, waveform classification, intermediate-depth earthquakes</p>

Shale, Quakes, and High Stakes: Regulating Fracking-Induced Seismicity in Oklahoma, USA and Lancashire, UK

2019 ◽  
Vol 3 (1) ◽  
pp. 1-14
Author(s):  
Miriam R. Aczel ◽  
Karen E. Makuch
Keyword(s):  
United States ◽  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Seismic Activity ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
High Volume ◽  
The United States ◽  
Horizontal Drilling ◽  
Induced Seismic Activity

High-volume hydraulic fracturing combined with horizontal drilling has “revolutionized” the United States’ oil and gas industry by allowing extraction of previously inaccessible oil and gas trapped in shale rock [1]. Although the United States has extracted shale gas in different states for several decades, the United Kingdom is in the early stages of developing its domestic shale gas resources, in the hopes of replicating the United States’ commercial success with the technologies [2, 3]. However, the extraction of shale gas using hydraulic fracturing and horizontal drilling poses potential risks to the environment and natural resources, human health, and communities and local livelihoods. Risks include contamination of water resources, air pollution, and induced seismic activity near shale gas operation sites. This paper examines the regulation of potential induced seismic activity in Oklahoma, USA, and Lancashire, UK, and concludes with recommendations for strengthening these protections.

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