Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

Theunissen, Thomas; Chevrot, Sébastien; Sylvander, Matthieu; Monteiller, Vadim; Calvet, Marie; Villaseñor, Antonio; Benahmed, Sébastien; Pauchet, Hélène; Grimaud, Frank

doi:10.1093/gji/ggx472

Cited by 27 publications

(28 citation statements)

References 70 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Second, we implement a new correction to account for the sphericity of the Earth which, if ignored, can yield traveltime errors of up to 1–2 s for raypaths exceeding 500 km. We chose the “sphere‐in‐a‐box” approach from Theunissen et al (). This approach calculates hypocenters and raypaths in a Cartesian coordinate system where the topography, station locations, and initial hypocenters are converted from latitude, longitude, and depth to the local left‐handed Cartesian coordinates x (azimuth 60°), y (azimuth 330°), and z (down) (Theunissen et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…We chose the “sphere‐in‐a‐box” approach from Theunissen et al (). This approach calculates hypocenters and raypaths in a Cartesian coordinate system where the topography, station locations, and initial hypocenters are converted from latitude, longitude, and depth to the local left‐handed Cartesian coordinates x (azimuth 60°), y (azimuth 330°), and z (down) (Theunissen et al, ). This way, we can represent the subduction zone and related seismicity in their true geometry.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography

2018

View full text Add to dashboard Cite

The Western Hellenic Subduction Zone is characterized by a transition from oceanic to continental subduction. In the southern oceanic portion of the system, abundant seismicity reaches depths of 100 km to 190 km, while the northern continental portion rarely exhibits deep earthquakes. Our study investigates how this oceanic‐continental transition affects fluid release and related seismicity along strike. We present results from local earthquake tomography and double‐difference relocation in conjunction with published images based on scattered teleseismic waves. Our tomographic images recover both subducting oceanic and continental crusts as low‐velocity layers on top of high‐velocity mantle. Although the northern and southern trenches are offset along the Kephalonia Transform Fault, continental and oceanic subducting crusts appear to align at depth. This suggests a smooth transition between slab retreat in the south and slab convergence in the north. Relocated hypocenters outline a single‐planed Wadati‐Benioff Zone with significant along‐strike variability in the south. Seismicity terminates abruptly north of the Kephalonia Transform Fault, likely reflecting the transition from oceanic to continental subducted crust. Near 90 km depth, the low‐velocity signature of the subducting crust fades out and the Wadati‐Benioff Zone thins and steepens, marking the outline of the basalt‐eclogite transition. Subarc melting of the mantle is only observed in the southernmost sector of the oceanic subduction, below the volcanic part of the arc. Beneath the nonvolcanic part, the overriding crust appears to have undergone large‐scale silica enrichment. This enrichment is observed as an anomalously low Vp/Vs ratio and requires massive transport of dehydration‐derived fluids updip through the subducting crust.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography

2018

View full text Add to dashboard Cite

show abstract

“…Thus, a 3-D velocity model that accommodates an in-situ status should be adopted. Many researchers have applied a high-resolution 3-D velocity model for earthquake locations [6], [17], [18] and microseismic event locations of reservoirs [19], [20], petroleum exploration [21] and rock slopes [22]. These results have demonstrated the 3-D model's advantages over a simple 1-D velocity model.…”

Section: A the Velocity Modelmentioning

confidence: 98%

Relocating Mining Microseismic Earthquakes in a 3-D Velocity Model Using a Windowed Cross-Correlation Technique

2020

View full text Add to dashboard Cite

Microseismic source location is a fundamental research interest in real-time microseismic monitoring and hazard risk assessment, and it provides the basis for determining the fracture zones and calculating seismic source parameters of the microseismicity (e.g., the event magnitude, the focal mechanism). In the present work, we carefully relocate some microseismic earthquakes that occurred in the Yongshaba mine (China) using the shooting 3-D ray-tracing (3D-RT) method based on a high-resolution 3-D velocity model, which is determined by a large amount of seismic data. Furthermore, a semiautomatic waveform cut method based on the cross-correlation (CC) technique (WCC) is developed for a quick, robust and precise determination of the direct P-phase relative delay times. Compared with the full waveform crosscorrelation (FWCC)-based method, the WCC-based method is free from the influence of complex later-phase waveform spectra. To verify the proposed method, we artificially generate the locations of 892 synthetic microseismic events, the P-phase travel times of which are calculated based on the given 3-D velocity model and the 3-D ray-tracing technique. The relocated hypocentres of these synthetic events obtained by the developed method are improved compared with those obtained by a homogeneous velocity model and the straight line-ray tracing based L1 norm time difference (TD) method (HV-SL-TD1), as well as those obtained by the 3-D velocity model and the straight line-ray tracing based L1 norm and L2 norm TD methods (3D-SL-TD1 and 3D-SL-TD2). Finally, we apply the proposed method to eight experimental blasts with pre-measured locations. The synthetic and application tests show that, despite some multi-path phenomena existing in the ray-tracing methods, the WCC-based method performs as well as the experienced manual picking method, and the results obtained by the 3D-RT location have smaller location errors (∼30 m) than those of the homogeneous velocity model-based methods (>40 m). The TD-based method is slightly better than the trigger time (TT)-based method when using the same norm, and the location precision of the L1 norm-based methods have a better resilience to larger picking errors than that of the L2 norm-based methods. Further improvements can be obtained by improving the resolution of the 3-D velocity model and including spatial voids in the model (e.g., tunnels and cavities) for the inversion.

show abstract

“…However, despite these difficulties, the systematic confrontation of the event depths with local networks optimally distributed above the seismicity (e.g. Perrot et al, 2005;Cushing et al, 2008;Got et al, 2011;Theunissen et al, 2018) suggests that the first order variations of the hypocentral depths of earthquakes at the scale of the territory appear to be interpretable. Fig.…”

Section: Overviewmentioning

confidence: 99%

A decade of seismicity in metropolitan France (2010–2019): the CEA/LDG methodologies and observations

Duverger¹,

Mazet‐Roux²,

Bollinger³

et al. 2021

BSGF - Earth Sci. Bull.

View full text Add to dashboard Cite

We summarize ten years of the French seismicity recorded by the Geophysical and Detection Laboratory (LDG) of the French Alternative Energies and Atomic Energy Commission (CEA) network from 2010 to 2019. During this period, 25,279 natural earthquakes were detected by the LDG and located within metropolitan France and its immediate vicinity. This seismicity contributes to more than 47% of the natural earthquakes instrumentally recorded since 1962 (mainly due to the improvement of network capacity), and includes about 28% of the most significant earthquakes with a magnitude ML ≥ 4.0. Recent seismic events therefore significantly expand the available national catalogues. The spatial distribution of 2010-2019 earthquakes is broadly similar to the previous instrumental pattern of the seismicity, with most of the seismic activity concentrated in the French Alps, the Pyrenees, the Brittany, the upper Rhine Graben and the Central Massif. A large part of the seismic activity is related to the occurrence of individual events. The largest earthquakes of the last ten years include the November 11, 2019 Le Teil earthquake with ML 5.4 and maximal epicentral intensities VII to VIII, which occurred in the Rhone valley; the April 28, 2016 La Rochelle earthquake with ML 5.2 and epicentral intensity V, which occurred at the southernmost extremity of the Armorican Massif in the vicinity of the Oléron island; and the April 7, 2014 Barcelonnette earthquake with ML 5.1 and epicentral intensity VII, which occurred in the Ubaye valley in the Alps. In 2019, two other moderate earthquakes of ML 5.1 and ML 4.9 stroke the western part of France, in Charente-Maritime and Maine-et-Loire department, respectively. The recent moderate earthquake occurrences and the large number of small earthquakes recorded give both the potential to revise some regional historical events and to determine more robust frequency-magnitude distributions, which are critical for seismic hazard assessment but complex due to low seismicity rates in France. The LDG seismic network installed since the early 1960s also allows a better characterization of the temporal structure of seismicity, partly diffused and in the form of mainshock-aftershocks sequences or transient swarms. These aspects are important in order to lower the uncertainties associated to seismogenic sources and improve the models in seismic hazard assessment for metropolitan France.

show abstract

Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

Cited by 27 publications

References 70 publications

Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography

Seismicity, Deformation, and Metamorphism in the Western Hellenic Subduction Zone: New Constraints From Tomography

Relocating Mining Microseismic Earthquakes in a 3-D Velocity Model Using a Windowed Cross-Correlation Technique

A decade of seismicity in metropolitan France (2010–2019): the CEA/LDG methodologies and observations

Contact Info

Product

Resources

About