Focal mechanism inversion in the Giudicarie–Lessini seismotectonic region (Southern Alps, Italy): Insights on tectonic stress and strain

2008 ◽  
Vol 460 (1-4) ◽  
pp. 106-115 ◽  
Author(s):  
Alfio Viganò ◽  
Gianni Bressan ◽  
Giorgio Ranalli ◽  
Silvana Martin
Keyword(s):  
Focal Mechanism ◽  
Tectonic Stress ◽  
Southern Alps ◽  
Stress And Strain

Geophysical Variables and Behavior: XXI. Geomagnetic Variation as Possible Enhancement Stimuli for UFO Reports Preceding Earthtremors

1985 ◽  
Vol 60 (1) ◽  
pp. 37-38 ◽  
Author(s):  
M. A. Persinger
Keyword(s):  
Tectonic Stress ◽  
Zero Order ◽  
Stress And Strain ◽  
Geomagnetic Variation ◽  
Shared Variance ◽  
And Behavior ◽  
Central Usa ◽  
New Madrid

The contribution of geomagnetic variation to the occurrence of UFORs (reports of UFOs) within the New Madrid States during the 6-mo. increments before increases in the numbers of IV-V or less intensity earthquakes within the central USA was determined. Although statistically significant zero-order correlations existed between measures of earthquakes, UFORs and geomagnetic variability, the association between the latter two deteriorated markedly when their shared variance with earthquakes was held constant. These outcomes are compatible with the hypothesis that geomagnetic variability (or phenomena associated with it) may enhance UFORs but only if tectonic stress and strain are increasing within the region.

Present state of tectonic stress of the Friuli area (eastern Southern Alps)

1998 ◽  
Vol 292 (3-4) ◽  
pp. 211-227 ◽  
Author(s):  
G Bressan ◽  
A Snidarcig ◽  
C Venturini
Keyword(s):  
Present State ◽  
Tectonic Stress ◽  
Southern Alps

Detailed statistical analysis of the Gole Larghe Fault Zone fracture network (Italian Southern Alps) improves estimates of the energy budget for intraplate earthquakes in basement rocks

2020 ◽  
Author(s):  
Andrea Bistacchi ◽  
Silvia Mittempergher ◽  
Steve A.F. Smith ◽  
Giulio Di Toro ◽  
Stefan Nielsen
Keyword(s):  
Fault Zone ◽  
Energy Budget ◽  
Fracture Network ◽  
Tectonic Stress ◽  
Southern Alps ◽  
Intraplate Earthquakes ◽  
Detailed Statistical Analysis ◽  
Distribution Studies ◽  
Fracture Distribution ◽  
Host Rocks

<p>We present a study on the paleoseismic Gole Larghe Fault Zone (GLFZ), composed of hundreds of sub-parallel faults hosted in tonalites of the Adamello Massif (Italian Southern Alps), where we collected a complete transect across the fault zone, including the background host rocks, over a thickness of >1km.</p><p>Along this transect, we studied the correlation between fracture spacing (for “fracture” here we mean joints, veins, faults, shear fractures, and all other brittle structures) and position with a robust non-parametric approach. This analysis, new for fracture distribution studies, allows detecting volumes of the fault zone with clustering or a trend in spacing, versus volumes where the spatial distribution is stationary. The analysis reveals that the GLFZ can be subdivided in “stationary volumes” where fractures shows stationary statistical properties. Each one of these volumes can be completely characterized with scanline and/or scanarea surveys to obtain a complete and statistically sound estimate of all fracture parameters (spacing, intensity, density, length, height, orientation, topology, etc.).</p><p>Within the GLFZ we have two main classes of structures: (i) “master” faults that are sub-parallel to the fault zone and are always characterized by pseudotachylytes and/or cataclasites, and (ii) minor “fractures” (e.g. Riedel fractures, joints, veins, etc.) that are oblique to the fault zone and interconnect the former. Out of the GLFZ we observe a background fracturing that is associated to the cooling of the Adamello tonalites under deviatoric tectonic stress (“cooling joints”).</p><p>By comparing fracture statistics within and outside the fault zone, we demonstrated that master faults within the GLFZ were almost completely inherited from the “cooling joints” of the host rocks. The cooling joints just grew in length and became completely interconnected at the scale of the seismic rupture. This means that, at least in the case of the GLFZ, the large faults and fractures along which seismic ruptures were running do not add significantly to the earthquake energy budget, because they were already present in the system before the onset of seismic activity. The only fractures to be considered in this budget are the minor interconnecting fractures (e.g. Riedel fractures, joints, veins, etc.) that are coated with pseudotachylytes.</p><p>These observations confirm once again the classical assumption that seismic ruptures propagate along pre-existing discontinuities and do not, in general, tend to fracture intact rocks.</p>

Study on Seismicity and Its Geodynamic Genesis in Ngari Areas

2020 ◽  
Author(s):  
Guangyin Xu ◽  
Qing Wu ◽  
Suyun Wang
Keyword(s):  
Stress Field ◽  
Focal Mechanism ◽  
Seismic Activity ◽  
Tectonic Stress ◽  
Earthquake Catalogue ◽  
Tectonic Stress Field ◽  
Eurasian Plate ◽  
The North ◽  
East Kunlun ◽  
Tectonic Belt

<p>The Ngari area in Tibet is in the forefront of land-continent collisions. The area is accompanied by the polymerization of plates, forming complex structures such as the Tethys Himalayan pleat belt, the Yarlung Zangbo suture belt, and the Gangdese continental margin magma arc from the south to the north. The multi-period dive collision-inland convergence process, the geological structure is complex and the seismicity is very high. Based on the Chinese historical earthquake catalogue, the China Modern Earthquake Catalogue and the seismic data from the International Seismological Center (ISC), we analyzed the seismic activity, focal mechanism and modern tectonic stress field in the Ngari area, and then analyzed the seismicity and its source of geodynamics. The main conclusions are as follows:(1) The seismic activities in the Ngari area are mainly distributed in the Himalayan tectonic belt, the Bangong-Nujiang tectonic belt, the Alkin-East Kunlun tectonic belt, and some near north-south trending tectonic belts; (2) Earthquakes near the Himalayan tectonic belt is dominated by reverse faulting events. The seismic activity near the Bangong-Nujiang tectonic belt and the Alkin-East Kunlun tectonic belt is dominated by strike-slip earthquakes. Near the north-south extensional tectonic belt, the earthquakes show as the normal faulting events. (3) The main direction of the modern tectonic stress field in the study area is near north-south direction; (4) Seismic activity, focal mechanism and modern tectonic stress field show that the geodynamic source in the Ngari region is from Collision and squeezing the between the Eurasian plate and the Indian Ocean plate.</p>

Joint inversion of source location and focal mechanism of microseismicity

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. KS41-KS49 ◽  
Author(s):  
Chuntao Liang ◽  
Yangyang Yu ◽  
Yihai Yang ◽  
Liang Kang ◽  
Chen Yin ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Focal Mechanism ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Optimal Solution ◽  
Effective Property ◽  
Stress And Strain ◽  
Data Set ◽  
As Stress ◽  
Scanning Algorithm

The seismic focal mechanism (FM) is an effective property to indicate source physics, as well as stress and strain distribution in regional, local, and microscales. We have developed an algorithm to jointly invert for the FM and source locations. For a given velocity structure, all possible combinations of source locations ([Formula: see text], [Formula: see text], and [Formula: see text]) and FM (strike, dip, and rake) were used to compute traveltimes and polarities of waveforms. Correcting normal moveout times and polarities and stacking all waveforms, the ([Formula: see text], [Formula: see text], [Formula: see text], strike, dip, and rake) combination that gave the strongest stacking power was identified as the optimal solution. Compared with the traditional source scanning algorithm (SSA) that only scanned source locations, this algorithm was thereby called the joint source scanning algorithm (jSSA). The jSSA method was tested rigorously, and it was applied to a hydraulic fracturing data set. Our work determined several advantages against the SSA method: (1) The jSSA method could identify many shear sources that could not be detected by the SSA method due to polarity variation; (2) the jSSA almost always yielded more events than the SSA method, and the added events could often provide much better characterization of the hydraulic fracturing; (3) the statistics of source mechanisms could provide additional knowledge on the orientation of fractures, as well as the local and regional stress and strain field; and (4) for those events that were detected by both methods, the stacking power of jSSA was always higher than that obtained in SSA.

scholarly journals Fault Geometry and Mechanism of the Mw 5.7 Nakchu Earthquake in Tibet Inferred from InSAR Observations and Stress Measurements

2021 ◽  
Vol 13 (24) ◽  
pp. 5142
Author(s):  
Yujiang Li ◽  
Yongsheng Li ◽  
Xingping Hu ◽  
Haoqing Liu
Keyword(s):  
Focal Mechanism ◽  
Historical Earthquakes ◽  
Tectonic Stress ◽  
Indian Plate ◽  
Coseismic Deformation ◽  
Normal Faulting ◽  
Eurasian Plate ◽  
Seismogenic Fault ◽  
Stress Measurements ◽  
Focal Mechanism Solutions

Different types of focal mechanism solutions for the 19 March 2021 Mw 5.7 Nakchu earthquake, Tibet, limit our understanding of this earthquake’s seismogenic mechanism and geodynamic process. In this study, the coseismic deformation field was determined and the geometric parameters of the seismogenic fault were inverted via Interferometric Synthetic Aperture Radar (InSAR) processing of Sentinel-1 data. The inversion results show that the focal mechanism solutions of the Nakchu earthquake are 237°/69°/−70° (strike/dip/rake), indicating that the seismogenic fault is a NEE-trending, NW-dipping fault dominated by the normal faulting with minor sinistral strike-slip components. The regional tectonic stress field derived from the in-situ stress measurements shows that the orientation of maximum principal compressive stress around the epicenter of the Nakchu earthquake is NNE, subparallel to the fault strike, which controlled the dominant normal faulting. The occurrence of seven M ≥ 7.0 historical earthquakes since the M 7.0 Shenza earthquake in 1934 caused a stress increase of 1.16 × 105 Pa at the hypocenter, which significantly advanced the occurrence of the Nakchu earthquake. Based on a comprehensive analysis of stress fields and focal mechanisms of the Nakchu earthquake, we propose that the dominated normal faulting occurs to accommodate the NE-trending compression of the Indian Plate to the Eurasian Plate and the strong historical earthquakes hastened the process. These results provide a theoretical basis for understanding the geometry and mechanics of the seismogenic fault that produced the Nakchu earthquake.

scholarly journals Microseismicity and stress in the vicinity of the Alpine Fault, central Southern Alps, New Zealand

2021 ◽  
Author(s):  
C Boese ◽  
John Townend ◽  
Euan Smith ◽  
Timothy Stern
Keyword(s):  
Focal Mechanism ◽  
Attenuation Factor ◽  
Strike Slip ◽  
Southern Alps ◽  
Active Deformation ◽  
Focal Mechanism Solutions ◽  
Alpine Fault ◽  
Horizontal Compressive Stress ◽  
American Geophysical ◽  
American Geophysical Union

We investigate present-day microseismicity associated with the central Alpine Fault and the zone of active deformation and uplift in the central Southern Alps. Using 14 months of data, robust hypocenter locations have been obtained for ∼1800 earthquakes of magnitudes between -0.3 and 4.2. We derived a magnitude scale with a frequency-dependent attenuation factor, γ(f) = γ0f, where γ0 = 1.89 ± 0.02 × 10-3 s/km, that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents. The maximum depth of the seismicity varies systematically with distance from the Alpine Fault, from 10 ± 2 km near the fault to 8 ± 2 km within 20 km and 15 ± 2 km further southeast. This distribution correlates with lateral variations in crustal resistivity: earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities >100 Ωm. Rocks at greater depth are too hot, too fluid-saturated, or too weak to produce detectable earthquakes. Focal mechanism solutions computed for 211 earthquakes (ML > 0.44) exhibit predominantly strike-slip mechanisms. We obtain a maximum horizontal compressive stress direction of 115 ± 10° from focal mechanism inversion. This azimuth is consistent with findings from elsewhere in the central and northern South Island, and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief. Our stress estimates suggest that the Alpine Fault (with a mean strike of 055°) is poorly oriented in an Andersonian sense but that individual thrust and strike-slip segments of the fault's surface trace have close to optimal orientations. Copyright 2012 by the American Geophysical Union.

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