Earthquake fault plane solutions near Vancouver Island

1979 ◽  
Vol 16 (3) ◽  
pp. 523-531 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
Fault Plane ◽  
Vancouver Island ◽  
Nodal Solutions ◽  
Island Region ◽  
Fault Plane Solutions ◽  
Principal Compressive Stress ◽  
Predominant Type ◽  
Shallow Earthquakes ◽  
Aftershock Sequences ◽  
Large Earthquakes

P nodal solutions for six earthquakes in the Vancouver Island region are consistent with a north–south orientation for the principal compressive stress. The predominant type of faulting is strike slip, either dextral slip on northwest striking faults or sinistral slip on northeast striking faults. The few aftershock sequences that can be documented for shallow earthquakes greater than magnitude 5 all contain very few aftershocks, which are small in size. This may indicate that higher than average stress drop is characteristic of large earthquakes in the Vancouver Island region.

The relation between fault plane solutions for earthquakes and the directions of the principal stresses

1969 ◽  
Vol 59 (2) ◽  
pp. 591-601
Author(s):  
Dan P. McKenzie
Keyword(s):  
Brittle Fracture ◽  
Stress Tensor ◽  
Principal Stress ◽  
Fault Plane ◽  
Triaxial Stress ◽  
Homogeneous Material ◽  
Principal Stresses ◽  
Fault Plane Solutions ◽  
Shallow Earthquakes ◽  
Earthquake Zone

abstract The stresses involved in shallow earthquakes and their occurrence along fault planes suggest that they occur by failure on weak planes, rather than by brittle fracture of a homogeneous material. Possible orientations of the stress tensor are examined to determine what limits fault plane solutions can place on the orientation of the greatest principal stress. For the general case of a triaxial stress, the only restriction is that this stress direction must lie in the quadrant containing P, but may be at right angles to the P direction. Thus shallow earthquakes impose a few limitations on the orientation of the stress tensor. In contrast the fault plane solutions from deep earthquakes are best explained by fracture of a homogeneous material, with the greatest principal stress directed down the dip of the earthquake zone.

The Oroville earthquake sequence of August 1975

1976 ◽  
Vol 66 (4) ◽  
pp. 1065-1084 ◽  
Author(s):  
Paul W. Morrison ◽  
Brian W. Stump ◽  
Robert Uhrhammer
Keyword(s):  
Sierra Nevada ◽  
Fault Plane ◽  
B Value ◽  
Earthquake Sequence ◽  
Occurrence Rate ◽  
California Department ◽  
Fault Plane Solutions ◽  
Aftershock Sequences ◽  
The University ◽  
The City

abstract The characteristics of the Oroville, California earthquake sequence of 1975 are presented. Historically, the Oroville area is one of low seismicity; the largest earthquake in the region occurred with a magnitude (ML) 5.7 in 1940 some 50 km north of Oroville. The first foreshock of the sequence occurred on June 28, 1975. Twnety-one foreshocks (ML ≧ 1.6), the largest of magnitude 4.7, preceded the magnitude 5.7 main shock of August 1. All foreshocks and aftershocks of ML ≧ 3.0 were located using seismographs operated by the University of California at Berkeley, USGS, and the California Department of Water Resources. The aftershock region covers an area approximately 14 by 10 km southeast of the city of Oroville. The depth distribution of the earthquakes indicates a west dipping fault plane. The b value of 0.61 shows the sequence to be rich in larger magnitude aftershocks. Similar b values have been determined for other aftershock sequences in California, such as a sequence near Coalinga in August 1975. The aftershock occurrence rate follows an Omori relation with n(t∞t−0.70. Apparent variability in the earthquake mechanisms of the series makes interpretation of composite fault-plane solutions difficult, but the data indicate normal faulting striking NNW and a west dip of about 30°–40°, the Sierra Nevada moving up with respect to the Great Valley.

Fault plane solutions of shallow earthquakes and contemporary tectonics in Asia

1973 ◽  
Vol 19 (2) ◽  
pp. 101-112 ◽  
Author(s):  
Peter Molnar ◽  
Thomas J. Fitch ◽  
Francis T. Wu
Keyword(s):  
Fault Plane ◽  
Fault Plane Solutions ◽  
Shallow Earthquakes

scholarly journals A holistic seismotectonic model of Delhi region

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Brijesh K. Bansal ◽  
Kapil Mohan ◽  
Mithila Verma ◽  
Anup K. Sutar
Keyword(s):  
Strain Energy ◽  
Fault Plane ◽  
Near Field ◽  
Energy Estimates ◽  
The West ◽  
Fault Plane Solutions ◽  
Northern India ◽  
Structural Environment ◽  
Reverse Faulting ◽  
Using Data

AbstractDelhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.

Microearthquake seismicity and tectonics of Coastal Northern California

1970 ◽  
Vol 60 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
Leonardo Seeber ◽  
Muawia Barazangi ◽  
Ali Nowroozi
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
San Andreas Fault ◽  
High Gain ◽  
Strike Slip ◽  
Fault System ◽  
Northern California ◽  
Fault Plane Solutions ◽  
Sharp Bend ◽  
San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

Aftershocks of the February 21, 1973 Point Mugu, California earthquake

1976 ◽  
Vol 66 (6) ◽  
pp. 1931-1952
Author(s):  
Donald J. Stierman ◽  
William L. Ellsworth
Keyword(s):  
Fault Zone ◽  
Main Shock ◽  
Fault Plane ◽  
Body Wave ◽  
P Wave ◽  
Fault System ◽  
Wave Radiation ◽  
Fault Plane Solutions ◽  
Complex Deformation ◽  
Transverse Ranges

abstract The ML 6.0 Point Mugu, California earthquake of February 21, 1973 and its aftershocks occurred within the complex fault system that bounds the southern front of the Transverse Ranges province of southern California. P-wave fault plane solutions for 51 events include reverse, strike slip and normal faulting mechanisms, indicating complex deformation within the 10-km broad fault zone. Hypocenters of 141 aftershocks fail to delineate any single fault plane clearly associated with the main shock rupture. Most aftershocks cluster in a region 5 km in diameter centered 5 km from the main shock hypocenter and well beyond the extent of fault rupture estimated from analysis of body-wave radiation. Strain release within the imbricate fault zone was controlled by slip on preexisting planes of weakness under the influence of a NE-SW compressive stress.

Microearthquakes in the Tihamat-Asir region of Saudi Arabia

1980 ◽  
Vol 70 (6) ◽  
pp. 2291-2293
Author(s):  
H. M. Merghelani ◽  
S. K. Gallanthine
Keyword(s):  
Saudi Arabia ◽  
Continental Crust ◽  
Red Sea ◽  
Fault Plane ◽  
Seismic Refraction ◽  
Earthquake Hazard ◽  
Tectonic Activity ◽  
Fault Plane Solutions ◽  
High Level ◽  
Asir Region

abstract During the course of a seismic refraction investigation in Saudi Arabia, an unexpected high level of microearthquake activity was detected near the border of the Red Sea and near the transition from oceanic to continental crust. The data is not adequate to determine fault plane solutions nor to relate the earthquakes to specific structures, but the existence of microearthquakes at this location suggest that there is a significant level of tectonic activity at a point 200 km from an axial trough of the Red Sea. These data, combined with other recent geological observations, may be an important clue to the understanding of continental rifting. The data suggest the need for a more thorough investigation of the earthquake hazard along the shores of the Red Sea.

The use of fisher statistics in fault plane solutions

1974 ◽  
Vol 64 (1) ◽  
pp. 279-283
Author(s):  
John Whitney ◽  
Ronald Merrill
Keyword(s):  
Fault Plane ◽  
Fault Plane Solutions
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