scholarly journals Faulting mechanism of the Campania–Lucania 1980 earthquake, Italy, from high-resolution, 3D velocity structure, aftershock relocation, fault-plane solutions, and post-seismic deformation modeling

2011 ◽  
Vol 54 (6) ◽  
Author(s):  
Antonella Amoruso ◽  
Luca Crescentini ◽  
Bellina Di Lieto ◽  
Roberto Scarpa
Keyword(s):  
High Resolution ◽  
Velocity Structure ◽  
Fault Plane ◽  
Fault Plane Solutions ◽  
Aftershock Relocation ◽  
Seismic Deformation

Slowly migrating tectonic microearthquake swarms in the Icelandic Rift Zone: driven by pore-pressure or aseismic slip transients?

2021 ◽  
Author(s):  
Tom Winder ◽  
Robert S White
Keyword(s):  
High Resolution ◽  
Rift Zone ◽  
Fault Plane ◽  
Plate Boundary ◽  
Double Difference ◽  
Aseismic Slip ◽  
Tectonic Earthquake ◽  
Fault Plane Solutions ◽  
Scaling Properties ◽  
Waveform Cross Correlation

<p>Intense swarms of microearthquakes have been detected in the rift zone of Central Iceland since the 1970s, but the cause of their clear swarm-like nature remains enigmatic. We use the QuakeMigrate earthquake detection and location software<sup>1</sup> to produce a highly complete catalogue of microseismicity from 2007-2020, using data from a dense local seismic network. Automatic hypocentre locations have been refined using waveform cross-correlation and double-difference relocation, and tightly constrained focal mechanisms have been obtained by manual analysis of a subset of events.</p><p>The resulting high-resolution earthquake catalogue reveals a network of conjugate strike-slip faults, oriented to accommodate plate-boundary extension. Sharply defined fault planes imaged by the microearthquake hypocentres range from 1-10 km in length, and are found between 1 and 8 km b.s.l., with their orientations closely matching the fault plane geometry inferred from the fault plane solutions. Seismicity within individual swarms displays a systematic migration of hypocentres at velocities of ~ 1 km/day. In the majority of swarms we also observe clusters of identical repeating events, providing evidence for re-loading of brittle asperities.</p><p>For a selection of swarms our high resolution seismic observations are complemented by GPS and InSAR measurements, allowing us to place constraints on the amount of fault slip. Comparing this, and the area of the fault plane activated in the swarm, to the seismic moment release reveals a significant contribution of aseismic slip, or very low effective stress drop. Analysis of swarms within this fault network triggered by the 2014 Bárðarbunga-Holuhraun dike intrusion provides further constraint on the amplitude of the stress cycle.</p><p>We combine our observations with comparisons to numerical & laboratory modelling studies, observed swarm scaling properties and knowledge of the geological and permeability structure of the Icelandic crust to determine the nature of the transient forcing driving these exceptionally well-recorded tectonic earthquake swarms.</p><p> </p><p>1: https://github.com/QuakeMigrate/QuakeMigrate Tom Winder, Conor Bacon, Jonathan D. Smith, Thomas S. Hudson, Julian Drew, & Robert S. White. (2021, January 15). QuakeMigrate v1.0.0 (Version v1.0.0). Zenodo. http://doi.org/10.5281/zenodo.4442749</p>

scholarly journals The rate of Seismic deformation in the Gulf of Aqaba as inferred from moment tensor summation

2020 ◽  
Author(s):  
Sattam Almadani
Keyword(s):  
Shear Deformation ◽  
Fault Plane ◽  
Moment Tensor ◽  
Strike Slip ◽  
Gulf Of Aqaba ◽  
Fault Plane Solutions ◽  
Seismicity Parameters ◽  
Fault Parameters ◽  
The Moment ◽  
Seismic Deformation

Abstract The main goal of this study is to quantify the rate of seismic deformation in the Gulf of Aqaba. The moment tensor summation technique based on the seismicity data, for all available historical and instrumental data (1900-2019), and reliable fault plane solutions was used to calculate the size and the shape of deformation. For the period from 1900 to 2019, the seismicity data was used to calculate the seismicity parameters (representing by the Gutenberg-Richter and moment-magnitude relations) and the spatial extent of the deformation zone. The fault parameters of forty-four earthquakes, having moment magnitudes range from 3.2 to 7.2, were used to construct the moment tensor summation and subsequently to calculate the rate of seismic deformation. The calculations showed that a predominant shear deformation acting in the Gulf of Aqaba is taken up by extension in a direction of N40.8 o E at a rate of 0.83±0.21 mm/yr. and compression in a direction of N131.6 o E at a rate of 0.32±0.05 mm/yr.; reflecting the Gulf of Aqaba is undergoing from shear deformation accommodated along a strike-slip fault. The obtained results exhibited that the present-day deformation in the Gulf of Aqaba is acting by the interaction of relative tectonic motions among African, Sinai and Arabia plates.

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

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.

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