scholarly journals Tracking subducted ridges through intermediate-depth seismicity in the Vanuatu subduction zone

Geology ◽  
2018 ◽  
Vol 46 (9) ◽  
pp. 767-770 ◽  
Author(s):  
Christian Baillard ◽  
Wayne C. Crawford ◽  
Valérie Ballu ◽  
Bernard Pelletier ◽  
Esline Garaebiti
Keyword(s):  
Subduction Zone ◽  
Intermediate Depth

Long-Term Interactions Between Intermediate Depth and Shallow Seismicity in North Chile Subduction Zone

2017 ◽  
Vol 44 (18) ◽  
pp. 9283-9292 ◽  
Author(s):  
Jorge Jara ◽  
Anne Socquet ◽  
David Marsan ◽  
Michel Bouchon
Keyword(s):  
Subduction Zone ◽  
Intermediate Depth

Improving Focal Mechanisms for Earthquakes in Taiwan Strait and Ryukyu Subduction Zone with Broadband Waveforms of Combined Networks

2020 ◽  
Author(s):  
Chieh-Chen Lee ◽  
Tai-Lin Tseng ◽  
Pei-Ru Jian
Keyword(s):  
Subduction Zone ◽  
Taiwan Strait ◽  
Focal Mechanisms ◽  
Passive Margin ◽  
Moho Depth ◽  
Offshore Area ◽  
Intermediate Depth ◽  
Velocity Models ◽  
Taiwan Shoal ◽  
Oblique Convergence

<p>  Taiwan region is a seismically active region formed by the oblique convergence between Philippine Sea Plate and Eurasia Plate. Focal mechanisms of most small-moderate sized earthquakes can be well constrained by the local seismic array, except for those occurred offshore Taiwan where azimuthal coverage is limited. To better understand the tectonic structures, it is desirable to improve the focal mechanisms using better located hypocenters, reasonable velocity models, and the best available stations. In this study we focus on the shallow earthquakes in Taiwan Strait and the intermediate-depth earthquakes in southernmost Ryukyu. Both regions are less explored but large historic events had been reported.</p><p>  For earthquakes in Taiwan Strait, we systematically studied earthquakes from 1996 to 2019, including the M<sub>w</sub>5.7 Taiwan Shoal sequence happened on 2018/11/25. A total of 22 new moment tensors (MTs) were resolved in the passive margin by combining Fujian and Taiwan seismic networks from either side of the strait. For events closer to Fujian, China, the velocity model with Moho depth of 35 km yields overall lower compensated linear vector dipole (CLVD) and acceptable misfit values; while as a 40 km thick crust is better for events closer to or on the shore of Taiwan. This Moho variation under the Taiwan Strait, although subtle, agrees well with the velocity structure constrained independently by previous studies. Earthquakes in the middle of the strait are dominant in strike-slip and normal slip within 30 km depth. Shallow thrusting events are found only in the Miaoli offshore area of Taiwan. As for the 2018 Taiwan Shoal earthquake sequence, it is located right on the region absence of known fault-plane solutions, therefore offers important new constraints. All events of the sequence show high angle strike-slips and shallow centroid depth of 11-21 km, more consistent with seismicity determined by Fujian seismic center. This event is far away from the M8 1604 Quanzhou earthquake, and is also clearly unrelated to the structure of 1994 M<sub>w </sub>6.7 normal-faulting event in Tainan Basin. The 2018 sequence is probably the reactivation of a pre-existing normal fault that was created by rifting during the Cenozoic.</p><p>  For future work, we will re-evaluate the MTs of M>5.5 intermediate-depth earthquakes of the Ryukyu subduction zone by including waveforms of stations YNG and IGK from Japan network in the inversion. We will also test different upper mantle velocities in the model for the computation of Green’s functions. We anticipate that our work can provide a set of parameters more suitable for the MT inversion, and the MT results can delineate the Ryukyu subduction zone properties better.</p><p> </p><p>keywords : Taiwan Strait, focal mechanisms, moment tensor inversion</p>

scholarly journals Slab stress field in the Hellenic subduction zone as inferred from intermediate-depth earthquakes

2011 ◽  
Vol 63 (2) ◽  
pp. 139-144 ◽  
Author(s):  
S. Rontogianni ◽  
K. I. Konstantinou ◽  
N. S. Melis ◽  
C. P. Evangelidis
Keyword(s):  
Stress Field ◽  
Subduction Zone ◽  
Intermediate Depth ◽  
Hellenic Subduction Zone ◽  
Slab Stress

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>

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