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

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.

Rampart seismic zone of central Alaska

1983 ◽  
Vol 73 (3) ◽  
pp. 813-829
Author(s):  
P. Yi-Fa Huang ◽  
N. N. Biswas
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
B Value ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Lithospheric Plate ◽  
Normal Faults ◽  
Seismic Zone ◽  
The West ◽  
Fault Plane Solutions

abstract This paper describes the characteristics of the Rampart seismic zone by means of the aftershock sequence of the Rampart earthquake (ML = 6.8) which occurred in central Alaska on 29 October 1968. The magnitudes of the aftershocks ranged from about 1.6 to 4.4 which yielded a b value of 0.96 ± 0.09. The locations of the aftershocks outline a NNE-SSW trending aftershock zone about 50 km long which coincides with the offset of the Kaltag fault from the Victoria Creek fault. The rupture zone dips steeply (≈80°) to the west and extends from the surface to a depth of about 10 km. Fault plane solutions for a group of selected aftershocks, which occurred over a period of 22 days after the main shock, show simultaneous occurrences of strike-slip and normal faults. A comparison of the trends in seismicity between the neighboring areas shows that the Rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central Alaska. The seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression.

scholarly journals A functional tool to explore the reliability of micro-earthquake focal mechanism solution for seismotectonic purposes

2021 ◽  
Author(s):  
Guido Maria Adinolfi ◽  
Raffaella De Matteis ◽  
Rita De Nardis ◽  
Aldo Zollo
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Focal Mechanisms ◽  
Seismic Network ◽  
Fault System ◽  
Focal Mechanism Solution ◽  
Fault Plane Solutions ◽  
Stress Regime ◽  
Focal Mechanism Solutions ◽  
Earthquake Focal Mechanism

Abstract. Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network used to monitor natural and/or induced micro-seismicity estimates focal mechanisms as function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P/S long-period spectral-level ratios and the P polarities to infer the fault-plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operated in the Campania-Lucania Apennines (Southern Italy) to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose can have a double purpose. It can be a valid tool to design or to test the performance of local seismic networks and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies.

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