scholarly journals Microseismic Focal Mechanisms and Implications for Changes in Stress during the 2014 Newberry EGS Stimulation

2019 ◽  
Vol 109 (5) ◽  
pp. 1653-1660 ◽  
Author(s):  
Ana C. Aguiar ◽  
Stephen C. Myers
Keyword(s):  
Maximum Stress ◽  
Sequence Data ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Fluid Injection ◽  
Waveform Cross Correlation ◽  
Reference Event ◽  
Maximum Horizontal Stress ◽  
East West

Abstract We adapt the relative polarity method from Shelly et al. (2016) to compute focal mechanisms for microearthquakes associated with the 2014 hydroshearing stimulation at the Newberry volcano geothermal site. We focus the analysis on events relocated by Aguiar and Myers (2018), who report that six event clusters predominantly comprise the 2014 sequence. Data quality allows focal mechanism analysis for four of the six event clusters. We use Hardebeck and Shearer (2002, 2003; hereafter HASH) to compute focal mechanisms based on first‐motion polarities and S/P amplitude ratios. We manually determine P‐ and S‐wave polarities for a well‐recorded reference event in each cluster, then use waveform cross correlation to determine whether recordings of other events in the cluster are the same or reversed polarity at each network station. Most waveform polarities are consistent with the affiliated reference event, indicating similar focal mechanisms within each cluster. The deeper clusters are east–west‐striking normal faults, whereas the shallower clusters, close to the top of the open‐hole section of the borehole, are strike slip with east–west motion. Regional studies and prestimulation borehole breakouts find the maximum stress direction is vertical and maximum horizontal stress is approximately north–south. Fault geometry and focal mechanisms of microseismicity during the stimulation suggest that increased pressure from fluid injection predominantly caused changes in horizontal stress, consistent with predictions from numerical studies of stress change caused by fluid injection. At shallow depths, where previous studies suggest the difference between vertical and horizontal stress is lowest, injection appears to have rotated the direction of maximum stress from vertical to horizontal, resulting in strike‐slip motion. At greater depth, vertical stress continued to be the dominant direction during the stimulation, but fault orientation indicates either reactivation of pre‐existing fractures or rotation of the direction of maximum horizontal stress from approximately north–south to east–west.

A New Uniform Moment Tensor Catalog for Yunnan, China, from January 2000 through December 2014

2020 ◽  
Vol 91 (2A) ◽  
pp. 891-900
Author(s):  
Yan Xu ◽  
Keith D. Koper ◽  
Relu Burlacu ◽  
Robert B. Herrmann ◽  
Dan-Ning Li
Keyword(s):  
Stress Field ◽  
Seismic Hazard ◽  
Moment Tensor ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Moment Tensors ◽  
Yunnan Region ◽  
Seismic Waveforms ◽  
The Moment ◽  
Maximum Horizontal Stress

Abstract Because of the collision of the Indian and Eurasian tectonic plates, the Yunnan Province of southwestern China has some of the highest levels of seismic hazard in the world. In such a region, a catalog of moment tensors is important for estimating seismic hazard and helping understand the regional seismotectonics. Here, we present a new uniform catalog of moment tensor solutions for the Yunnan region. Using a grid-search technique to invert seismic waveforms recorded by the permanent regional network in Yunnan and the 2 yr ChinArray deployment, we present 1833 moment tensor solutions for small-to-moderate earthquakes that occurred between January 2000 and December 2014. Moment magnitudes in the new catalog vary from Mw 2.2 to 6.1, and the catalog is complete above Mw∼3.5–3.6. The moment tensors are constrained to be purely double-couple and show a variety of faulting mechanisms. Normal faulting events are mainly concentrated in northwest Yunnan, while farther south along the Sagaing fault the earthquakes are mostly thrust and strike slip. The remaining area includes all three styles of faulting but mostly strike slip. We invert the moment tensors for the regional stress field and find a strong correlation between spatially varying maximum horizontal stress and Global Positioning System observations of horizontal ground velocity. The stress field reveals clockwise rotation around the eastern Himalayan syntaxis, with northwest–southeast compression to the east of the Red River fault changing to northeast–southwest compression west of the fault. Almost 88% of the centroid depths are shallower than 16 km, consistent with a weak and ductile lower crust.

PRESENT-DAY STATE-OF-STRESS OF SOUTHEAST AUSTRALIA

2006 ◽  
Vol 46 (1) ◽  
pp. 283 ◽  
Author(s):  
E. Nelson ◽  
R. Hillis ◽  
M. Sandiford ◽  
S. Reynolds ◽  
S. Mildren
Keyword(s):  
Focal Mechanism ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanism Solutions ◽  
Southeast Australia ◽  
State Of Stress ◽  
Earthquake Focal Mechanism ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress ◽  
Gippsland Basin

There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area.Analysis of existing and new data from petroleum wells reveals broadly northwest–southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.

A seismological study of two Attica, New York earthquakes

1978 ◽  
Vol 68 (3) ◽  
pp. 641-651 ◽  
Author(s):  
Robert B. Herrmann
Keyword(s):  
New York ◽  
Source Parameters ◽  
Focal Depth ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
The Other ◽  
Nodal Plane ◽  
Reverse Faulting ◽  
Epicentral Intensity ◽  
East West

abstract The Attica, New York earthquakes of January 1, 1966 and June 12, 1967 are studied in detail to obtain their focal mechanisms, depths and seismic moments. Both events have similar source parameters with one nodal plane striking about 120° and dipping 60°S and the other nodal plane striking about 20° and dipping 70°E. The fault motion on the NNE nodal plane has a component of right lateral strike slip and one of reverse faulting. Though this nodal plane parallels the Clarendon-Linden structure, the possibility of associating the other nodal plane with a diffuse east-west seismicity trend cannot be excluded. The shallow focal depth of 2 to 3 km for these two events can be used as an explanation of the relatively high epicentral intensity VIII of the Attica event of 1929.

Waveform Cross-Correlation Relocation and Focal Mechanisms for the 2019 Ridgecrest Earthquake Sequence

2020 ◽  
Vol 91 (4) ◽  
pp. 2055-2061 ◽  
Author(s):  
Guoqing Lin
Keyword(s):  
Cross Correlation ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Volcanic Field ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Earthquake Sequence ◽  
Waveform Data ◽  
Waveform Cross Correlation ◽  
First Motion

Abstract I present a high-precision earthquake relocation catalog and first-motion focal mechanisms before and during the 2019 Ridgecrest earthquake sequence in eastern California. I obtain phase arrivals, first-motion polarities, and waveform data from the Southern California Earthquake Data Center for more than 24,000 earthquakes with the magnitudes varying between −0.7 and 7.1 from 1 January to 31 July 2019. I first relocate all the earthquakes using phase arrivals through a previously developed 3D seismic-velocity model and then improve relative location accuracies using differential times from waveform cross correlation. The majority of the relocated seismicity is distributed above 12 km depth. The seismicity migration along the northwest–southeast direction can be clearly seen with an aseismic zone near the Coso volcanic field. Focal mechanisms are solved for all the relocated events based on the first-motion polarity data with dominant strike-slip fault solutions. The Mw 6.4 and 7.1 earthquakes are positioned at 12.45 and 4.16 km depths after the 3D relocation, respectively, with strike-slip focal solutions. These results can help our understanding of the 2019 Ridgecrest earthquake sequence and can be used in other seismological and geophysical studies.

Graphics Processing Unit-Based Match and Locate (GPU-M&L): An Improved Match and Locate Method and Its Application

2020 ◽  
Vol 91 (2A) ◽  
pp. 1019-1029 ◽  
Author(s):  
Min Liu ◽  
Hongyi Li ◽  
Miao Zhang ◽  
Tongli Wang
Keyword(s):  
Graphics Processing Unit ◽  
Weighting Factor ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Processing Unit ◽  
Detection Ability ◽  
Central Processing ◽  
China Earthquake ◽  
Graphics Processing ◽  
East West

Abstract Microearthquake detection and location are critical for understanding earthquake mechanisms and mitigating seismic hazards. Match and locate (M&L) is an effective method for simultaneously detecting and locating small earthquakes. However, the heavy computational demands of the M&L make it challenging to apply to big data. In this article, we develop an improved M&L method—called graphics processing unit-based M&L (GPU-M&L). The GPU-M&L differs from the M&L in two ways: (1) adding weighting factor for each component of templates to improve the detection ability and (2) implementing the M&L method on GPU to accelerate the computation. Synthetic tests show the GPU-M&L can not only handle smaller earthquakes than the M&L but also perform 4.5 times faster than the M&L parallelly programed on central processing unit. As an example, we utilize the GPU-M&L to study the seismic activity during seven days after the 2015 Ms 5.8 Alxa, China, earthquake (from 15 to 21 April 2015). Using 38 cataloged earthquakes as templates, we detect ∼20 times more events than in the routine catalog. The distribution of those detected events, along with focal mechanisms of large events, suggests that the 2015 Ms 5.8 earthquake occurred on an east–west-trending hidden strike-slip fault.

Hydraulic stimulation of natural fractures as revealed by induced microearthquakes, Carthage Cotton Valley gas field, east Texas

Geophysics ◽  
2003 ◽  
Vol 68 (2) ◽  
pp. 441-452 ◽  
Author(s):  
James T. Rutledge ◽  
W. Scott Phillips
Keyword(s):  
Hydraulic Fracture ◽  
Fracture Zone ◽  
Horizontal Stress ◽  
Focal Mechanisms ◽  
Fracture Plane ◽  
Natural Fractures ◽  
East Texas ◽  
Gas Field ◽  
Cotton Valley ◽  
Maximum Horizontal Stress

We produced a high‐resolution microseismic image of a hydraulic fracture stimulation in the Carthage Cotton Valley gas field of east Texas. We improved the precision of microseismic event locations four‐fold over initial locations by manually repicking the traveltimes in a spatial sequence, allowing us to visually correlate waveforms of adjacent sources. The new locations show vertical containment within individual, targeted sands, suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80‐m section. Treatment (i.e., fracture‐zone) lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals. The highest quality locations indicate fracture‐zone widths as narrow as 6 m. Similarity of adjacent‐source waveforms, along with systematic changes of phase amplitude ratios and polarities, indicate fairly uniform source mechanisms (fracture plane orientation and sense of slip) over the treatment length. Composite focal mechanisms indicate both left‐ and right‐lateral strike‐slip faulting along near‐vertical fractures that strike subparallel to maximum horizontal stress. The focal mechanisms and event locations are consistent with activation of the reservoir's prevalent natural fractures, fractures that are isolated within individual sands and trend subparallel to the expected hydraulic fracture orientation (maximum horizontal stress direction). Shear activation of these fractures indicates a stronger correlation of induced seismicity with low‐impedance flow paths than is normally found or assumed during injection stimulation.

Microearthquakes in the Mono Lake-Northern Owens Valley, California, region from September 28 to October 18, 1970

1975 ◽  
Vol 65 (4) ◽  
pp. 835-844
Author(s):  
A. M. Pitt ◽  
Don W. Steeples
Keyword(s):  
Strike Slip ◽  
Focal Mechanisms ◽  
Mono Lake ◽  
Owens Valley ◽  
Lateral Strike Slip ◽  
Tension Axis ◽  
Seismograph Network ◽  
Historic Seismicity ◽  
East West ◽  
The U.S

Abstract A portable seismograph network was operated by the U.S. Geological Survey in the Mono Lake-northern Owens Valley, California, region in the autumn of 1970. From 20 days of recording, 74 microearthquakes were located. The geographic extent of the microearthquakes is similar to the historic seismicity from 1934 to 1970. Focal mechanisms are mostly right-lateral strike slip; one very good dip-slip solution was obtained. The relative tension axis was found to be very nearly east-west.

Le bassin de Tizi n'Test (Haut Atlas, Maroc) : exemple d'évolution d'un segment oblique au rift de l'Atlantique central au Trias

2003 ◽  
Vol 40 (7) ◽  
pp. 949-964 ◽  
Author(s):  
Abdelmounim Qarbous ◽  
Fida Medina ◽  
Christian Hoepffner
Keyword(s):  
Fault Zone ◽  
Inverse Analysis ◽  
Horizontal Stress ◽  
Strike Slip ◽  
High Atlas ◽  
State Of Stress ◽  
Minimum Stress ◽  
Maximum Horizontal Stress ◽  
Central Atlantic

Detailed mapping completed by a microtectonic study of the Tizi n'Test Triassic basin, located along the Tizi n'Test fault zone in the Moroccan High Atlas, has allowed us to improve the knowledge on the geometry of the structures and the activity of faults during the Triassic extensional events related to the rifting of the central Atlantic. The latter are reflected by the development of a rift, at present inverted and deformed by the collision of Africa and Europe, comprising kilometric-scale grabens and half-grabens bounded by major faults trending ENE–WSW, with a dip towards the NNW, and a dip-slip syndepositional motion. Inverse analysis of fault slickenside populations shows a heterogeneous Triassic state of stress. However, in the most significant measurement sites, the maximum horizontal stress σ1 is vertical, while the minimum stress σ3 is horizontal with a NW–SE trend. The strike-slip component appears to be very small during the Triassic, a noticeable fact because of the obliquity of the basin with respect to the Atlantic rift.

scholarly journals Crustal Strain and Stress Fields in Egypt from Geodetic and Seismological Data

2021 ◽  
Vol 13 (7) ◽  
pp. 1398
Author(s):  
Mohamed Rashwan ◽  
Rashad Sawires ◽  
Ali M. Radwan ◽  
Federica Sparacino ◽  
José Antonio Peláez ◽  
...  
Keyword(s):  
Stress Field ◽  
Large Scale ◽  
Nile Delta ◽  
Plate Boundary ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Surface Strain ◽  
Gulf Of Aqaba ◽  
Seismological Data ◽  
Maximum Horizontal Stress

The comparison between crustal stress and surface strain azimuthal patterns has provided new insights into several complex tectonic settings worldwide. Here, we performed such a comparison for Egypt taking into account updated datasets of seismological and geodetic observations. In north-eastern Egypt, the stress field shows a fan-shaped azimuthal pattern with a WNW–ESE orientation on the Cairo region, which progressively rotated to NW–SE along the Gulf of Aqaba. The stress field shows a prevailing normal faulting regime, however, along the Sinai/Arabia plate boundary it coexists with a strike–slip faulting one (σ1 ≅ σ2 > σ3), while on the Gulf of Suez, it is characterized by crustal extension occurring on near-orthogonal directions (σ1 > σ2 ≅ σ3). On the Nile Delta, the maximum horizontal stress (SHmax) pattern shows scattered orientations, while on the Aswan region, it has a WNW–ESE strike with pure strike–slip features. The strain-rate field shows the largest values along the Red Sea and the Sinai/Arabia plate boundary. Crustal stretching (up to 40 nanostrain/yr) occurs on these areas with WSW–ENE and NE–SW orientations, while crustal contraction occurs on northern Nile Delta (10 nanostrain/yr) and offshore (~35 nanostrain/yr) with E–W and N–S orientations, respectively. The comparison between stress and strain orientations over the investigated area reveals that both patterns are near-parallel and driven by the same large-scale tectonic processes.

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