scholarly journals The horse canyon earthquake of August 2, 1975—Two-stage stress-release process in a strike-slip earthquake

1979 ◽  
Vol 69 (4) ◽  
pp. 1161-1173
Author(s):  
Stephen Hartzell ◽  
James N. Brune
Keyword(s):  
Rise Time ◽  
Stress Drop ◽  
Body Wave ◽  
Strike Slip ◽  
Fault System ◽  
Stress Release ◽  
Two Stage ◽  
Source Radius ◽  
Wide Range ◽  
Stress Drops

abstract A moderate strike-slip earthquake (ML = 4.8) occurred on the San Jacinto fault system about 60 km northwest of the Salton Sea on August 2, 1975. Analysis of main shock and aftershock data suggest that stress release during this earthquake took place in two stages. During one stage faulting occurred over a relatively small source area (source radius of ∼0.5 km), with a rapid dislocaton rate (rise time ∼0.1 sec), possibly associated with an asperity on the fault. During the second stage of faulting, the rupture front grew, but at a much slower rate (rise time ∼10 sec), to a final source radius of ∼1.0 km. The above model explains the larger moment estimate based on 20-sec surface waves compared to shorter period body-wave estimates, and also the apparent increase in source dimension with time. The model allows for large stress drops over small source dimensions, but when averaged over the final extent of the rupture plane, stress drops are much lower. The rupture of the asperity is characterized by a moment of 6.5 × 1022 dyne-cm and a stress drop of about 225 bars. The total moment is about 3.0 × 1023 dyne-cm with an averaged stress drop over the fault plane of approximately 90 bars and a dislocation of 25 cm. Observations similar to the ones reported on here have been noted for other earthquakes with a wide range of magnitudes, including: a few large earthquakes in Japan, the 1971 San Fernando earthquake and some of its aftershocks, the 1975 Oroville earthquake, and some swarm events in the Imperial Valley. These observations suggest that a two-stage rupture mechanism may be a fairly common occurrence in shallow faulting and may reflect possible large variations in stress over a length scale of kilometers within the crust.

Aftershock stress release along active fault planes of the 1984 Round Valley, California, earthquake sequence applying a time-domain stress drop method

1993 ◽  
Vol 83 (1) ◽  
pp. 144-159 ◽  
Author(s):  
Kenneth D. Smith ◽  
Keith F. Priestley
Keyword(s):  
Stress Drop ◽  
Pulse Width ◽  
Active Fault ◽  
Fault Plane ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Stress Release ◽  
Rupture Surface ◽  
Stress Drops ◽  
Conjugate Fault

Abstract The 23 November 1984 ML 5.8 Round Valley earthquake is one in a series of moderate (ML ≈ 6) earthquakes to have occurred in the Bishop-Mammoth Lakes, California, area since 1978. This earthquake and its aftershock sequence occurred within a dense seismic network, and hypocentral location quality is excellent. In a previous study, we determined that the Round Valley sequence involved faulting on a conjugate set of fault planes; one, a near-vertical plane striking N30°E, the mainshock fault plane showing principally left-lateral strike-slip motion, and another subperpendicular to the mainshock fault plane striking N40°W and dipping 55°NE, exhibiting dominantly right-lateral strike slip. This conjugate fault plane conforms to a postulated extension of the Hilton Creek fault and is the only significant activity on this structure in the 12-year Bishop-Mammoth Lakes earthquake sequence. Source dimensions and stress drops for 87 aftershocks (ML 2.8 to 4.2) of the Round Valley sequence have been determined using an adaptation of the initial P-wave pulse width time-domain deconvolution technique of Frankel and Kanamori (1983). The aftershock sequence is confined to a limited volume of crust. We have shown that site and instrument effects and not whole-path attenuation control the minimum pulse widths for this limited region. The determination of a site minimum pulse width, rather than a minimum pulse width for each source receiver pair as in the Frankel and Kanamori study, makes the deconvolution procedure practical for processing the large numbers of events in an aftershock sequence. With the large data set available for the Round Valley aftershock sequence, patterns of the stress drop along the active fault planes can be seen in detail. Source radii systematically increase with magnitude from about 100 m for events near magnitude 3.0 to 500 m for events near magnitude 4.0. Static stress drops range from 10 to 200 bars and are not strongly correlated with magnitude or depth. The stress release pattern reveals a broad stress drop low (Δσ ≈ 10 bars) for aftershocks within the mainshock fault plane that is consistent with other evidence of the rupture surface of the Round Valley mainshock. Higher stress release occurs above and below the mainshock rupture surface and on the shallower, conjugate fault plane. Further distant from the rupture surface of the mainshock, stress drops decrease to average values. On the conjugate fault surface, stress drops are seen to be high in areas that may be interpreted as “off-fault” clusters with respect to the mainshock rupture surface.

​Slip modes and interaction in a simplified strike-slip fault system with increasing geometrical complexity

2021 ◽  
Author(s):  
Michael Rudolf ◽  
Joscha Podlesny ◽  
Esther Heckenbach ◽  
Matthias Rosenau ◽  
Anne Glerum ◽  
...  
Keyword(s):  
Strike Slip ◽  
Fault System ◽  
Scaling Relations ◽  
Stick Slip ◽  
Multiple Faults ◽  
Fault Surface ◽  
Magnitude Scaling ◽  
Geometrical Complexity ◽  
Wide Range ◽  
Fault Heterogeneity

<p>The release of elastic energy along an active fault is accommodated by a wide range of slip modes. It ranges from long-term slow slip events (SSEs) and creep to short-term tremors and earthquakes. They vary not only in their characteristic duration but also in their magnitude, spatial exten<span><span>t</span></span> and slip velocities. The exact relationship is unclear, as in some regions many slip modes occur simultaneously (e.g. Tohoku-Oki) and in others certain slip modes are completely absent (e.g. Cascadia).</p><p>One of the driving factors in the generation of this large variety of slip modes is the interplay of fault heterogeneity and geometrical complexity of the fault system. We test various settings in terms of fault heterogeneity and geometrical complexity with a scaled physical model. The experimental results are then validated and benchmarked through multi-scale numerical simulations. We describe <span><span>the</span></span> system using <span><span>a</span></span> rate-and-state frictional framework and introduce on-fault heterogeneity with variable frictional properties. All properties are the same for analogue and numerical simulation as far as they can be determined or realized experimentally (a-b, v<sub>load</sub>, S<sub>hmax</sub>, S<sub>hmin</sub>, etc...). As analogue material we use segmented, decimetre sized neoprene foam blocks in multiple configurations (e.g. biaxial shear at forces <1 kN) to simulate the elastic upper crust. The contact surfaces are spray-painted with acrylic paint to generate velocity weakening characteristics in between the blocks which is similar to the frictional behaviour of natural faults. We add heterogeneity to the fault surface by varying the fault area that is velocity weakening using grease. Geometrical complexity is implemented using conjugated or parallel sets of additional faults with the same characteristics.</p><p>We are able to reliably generate frequent stick-slip events of variable size and recurrence intervals. The slip characteristics, such as slip distribution, are in good agreement with analytical solutions of fault slip in elastic media. In a geometrically simple strike-slip model the recurrence behaviour and magnitude follows straightforward scaling relations in accordance with existing studies. If geometrical complexity is added to the model we observe clustering and variable recurrence that differ from the simpler geometry. Additionally, we are going to give an outlook on the interaction behaviour of multiple faults in dependence of their geometric configuration and the generation of power-law type magnitude scaling relations.</p>

scholarly journals Earthquake Source Characteristics and S-Wave Propagation Attenuation in the Junction of the Northwest Tarim Basin and Kepingtage Fold-and-Thrust Zone

2020 ◽  
Vol 8 ◽  
Author(s):  
Hongwei Wang ◽  
Ruizhi Wen
Keyword(s):  
Tarim Basin ◽  
Stress Drop ◽  
Corner Frequency ◽  
Stress Release ◽  
S Wave ◽  
Study Region ◽  
Source Characteristics ◽  
Thrust Zone ◽  
Source Spectra ◽  
Stress Drops

We separated the propagation path attenuation and source spectra from the S-wave Fourier amplitude spectra of the observed ground motions recorded during 46 small-to-moderate earthquakes in the junction of the northwest Tarim Basin and Kepingtage fold-and-thrust zone, mainly composed of two Jiashi seismic sequences in 2020 and 2018. Slow seismic wave decay was observed as the distance increased, while the quality factor regressed as 60.066 f0.988 for frequency f = 0.254–30 Hz reflects the strong anelastic attenuation in the study region. We estimated the stress drops for the 46 earthquakes under investigation from the preferred corner frequencies and seismic moments by fitting the inverted source spectra and the theoretical ω-square model. The relationship between seismic moment and corner frequency and the dependence of the stress drop on the moment magnitude reveal the breakdown of earthquake self-similar scaling for the events in this study. The temporal variation in stress drops indicates that the mainshock plays a short-term role in the source characteristics of the surrounding earthquakes. Aftershocks immediately following the mainshock show a low stress release and then gradually recover in a short time. The healing process for the fractured fault in the mainshock may be one reason for the stress drop recovery of the aftershock. The foreshock with the low stress release occurring in the high-heterogeneity fault zone may motivate the following occurrence of the largest magnitude mainshock with a high stress drop. We inferred that the foreshock-mainshock behavior, including several moderate events, may be predisposed to occur in our study region characterized by an inhomogeneous crust.

Characterization of Major Fault Systems in the Kachchh Intraplate Region, Gujarat, India, by Focal Mechanism and Source Parameters

2020 ◽  
Vol 91 (6) ◽  
pp. 3496-3517
Author(s):  
Charu Kamra ◽  
Sumer Chopra ◽  
Ram Bichar Singh Yadav ◽  
Vishwa Joshi
Keyword(s):  
Focal Mechanism ◽  
Stress Drop ◽  
Source Parameters ◽  
Strike Slip ◽  
Average Stress ◽  
Fault System ◽  
Rift Basin ◽  
Fault Systems ◽  
Major Fault

Abstract The focal mechanism and source parameters of 41 local earthquakes (Mw 4.0–5.1) that occurred in the Kachchh rift basin, which is seismically one of India’s most active intraplate regions, are determined to characterize various active fault systems in that region. The tectonics in the rift basin are heterogeneous and complex. In the present study, it was found that one-third of the earthquakes exhibit reverse mechanism and three-fourth are either strike slip or have some components of strike slip. Thus, we conclude that transverse tectonics are currently dominant in the Kachchh rift. These transverse faults are preferably oriented in the northeast–southwest and northwest–southeast directions in the eastern and western parts of the rift, respectively. The movement is sinistral and dextral on faults that are oriented in the northeast–southwest and northwest–southeast directions, respectively. These transverse faults are almost vertical (dip>70°) and mostly blind with no surface expressions. Most of the significant faults that strike east–west dip toward the south and are listric. The stress drop of these 41 earthquakes ranges between 2.3 and 10.39 MPa. It was found that the stress drop of earthquakes may depend on the focal mechanism and is independent of focal depths. The average stress drop is found to be the highest (7.3 MPa) for the earthquakes that show a dominant normal mechanism accompanied by strike slip (5.4 MPa) and reverse (4.7 MPa). The average stress drop of the Kachchh intraplate region is 5.3 MPa, which is consistent with other intraplate regions of the world. A conceptual model of the fault system in the Kachchh region is proposed, based on the results obtained in the present study.

scholarly journals Broadband waveform observation of the 28 June 1991 Sierra Madre earthquake sequence (ML = 5.8)

1994 ◽  
Vol 84 (6) ◽  
pp. 1725-1738 ◽  
Author(s):  
Kuo-Fong Ma ◽  
Hiroo Kanamori
Keyword(s):  
Stress Drop ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Earthquake Sequence ◽  
High Quality ◽  
San Gabriel Mountains ◽  
Motion Data ◽  
Sierra Madre ◽  
First Motion ◽  
Stress Drops

Abstract The Sierra Madre earthquake (MI = 5.8) of 28 June 1991 occurred at a depth of about 12 km, on the Clamshell-Sawpit fault in the San Gabriel Mountains. High-quality seismograms were recorded with TERRAscope not only for the mainshock but also for the aftershocks at epicentral distances of about 16 km. We determined the focal mechanisms and seismic moments of the mainshock and 21 aftershocks by combining the waveform and first-motion data. We classified the events into five groups according to the location and waveforms recorded at PAS. Most events located within 5 km west of the mainshock are similar to the mainshock in waveform. The mechanisms thus determined are thrust mechanisms. A few events located east of the mainshock have waveforms different from the mainshock and have strike-slip mechanisms. The average Qβ values along the paths from the hypocenters of the Sierra Madre and the 3 December 1988 Pasadena earthquake (ML = 4.9) to PAS are about 130 and 80, respectively. The stress drop of the mainshock is about 500 bars. Most of the aftershocks have stress drops between 10 and 100 bars.

scholarly journals A low-stress-drop, low-magnitude earthquake with surface faulting: The Imperial, California, earthquake of March 4, 1966

1967 ◽  
Vol 57 (3) ◽  
pp. 501-514 ◽  
Author(s):  
James N. Brune ◽  
Clarence R. Allen
Keyword(s):  
Stress Drop ◽  
Strong Support ◽  
Surface Displacement ◽  
Love Waves ◽  
Field Observations ◽  
Center Line ◽  
High Excitation ◽  
Magnitude Range ◽  
Wide Range ◽  
Stress Drops

abstract Right-lateral surface displacement reaching 1 1/2 centimeters occurred over a ten-kilometer section of the Imperial fault in association with a magnitude 3.6 earthquake on March 4, 1966, the smallest known earthquake yet associated with surface displacement. The displacement is documented by field observations of en-echelon cracking in pavement and the offset of the white center line of Highway 80. The association of the observed displacement with the March 4 earthquake is supported by the shallow depth of the earthquake source, the high excitation of waves in the top layer of sediments, the high excitation of Love waves of period 8-15 seconds, the distribution of aftershocks, and the agreement between the source moment as calculated from the observed faulting and from the amplitudes of Love waves. Calculations based on faulting theory indicate a fault depth of 1.1 km, a net moment of 2 × 1022 dyne-cm, a stress drop of 1.1 bar and an energy release of 1017 ergs. The remarkable internal consistency of the various calculations provides strong support for the faulting mechanism. It is suggested that low stress drops and relatively large fault lengths may be associated with many other small earthquakes and that allowance must be made for a wide range in the stress drops and fault lengths for any given magnitude range.

Is the North Altyn fault part of a strike-slip duplex along the Altyn Tagh fault system?

Geology ◽  
2000 ◽  
Vol 28 (3) ◽  
pp. 255 ◽  
Author(s):  
Eric Cowgill ◽  
An Yin ◽  
Wang Xiao Feng ◽  
Zhang Qing
Keyword(s):  
Strike Slip ◽  
Fault System ◽  
Altyn Tagh Fault ◽  
The North ◽  
Altyn Tagh

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.

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