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.

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.

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.

Aftershock sequence and focal parameters of the February 28, 1969 earthquake of the Azores-Gibraltar fracture zone

1972 ◽  
Vol 62 (3) ◽  
pp. 699-719 ◽  
Author(s):  
A. López Arroyo ◽  
A. Udías
Keyword(s):  
Canary Islands ◽  
Fracture Zone ◽  
Main Shock ◽  
Fault Plane ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Strait Of Gibraltar ◽  
Wide Region ◽  
Focal Parameters ◽  
Source Mechanism Solution

Abstract The earthquake of February 28, 1969, which occurred about 500 km west of the Strait of Gibraltar, was felt over the entire Iberian Peninsula, in a wide region of Morocco, and south to the Canary Islands. It had a long sequence of aftershocks continuing for at least 10 months, but, nevertheless, most of the energy seems to have been liberated in the main shock of which the mb was 7.4. The source mechanism solution indicates a fault plane striking N 67°W and dipping 68°SW, with motion principally of the strike-slip type. There also is some overthrusting. The horizontal extent of faulting is of the order of 90 km.

scholarly journals The 1991 Sierra Madre earthquake sequence in southern California: Seismological and tectonic analysis

1994 ◽  
Vol 84 (4) ◽  
pp. 1058-1074 ◽  
Author(s):  
Egill Hauksson
Keyword(s):  
Los Angeles ◽  
Fault Plane ◽  
B Value ◽  
Tectonic Stress ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Stress Axis ◽  
The North ◽  
Sierra Madre

Abstract The (ML 5.8) Sierra Madre earthquake of 28 June 1991 occurred at a depth of 12 km under the San Gabriel Mountains of the central Transverse Ranges. Since at least 1932 this region had been quiescent for M ≧ 3. The mainshock focal mechanism derived from first-motion polarities exhibited almost pure thrust faulting, with a rake of 82° on a plane striking N62°E and dipping 50° to the north. The event appears to have occurred on the Clamshell-Sawpit fault, a splay of the Sierra Madre fault zone. The aftershock sequence following the mainshock occurred at a depth of 9 to 14 km and was deficient in small earthquakes, having a b value of 0.6. Twenty nine single-event focal mechanisms were determined for aftershocks of M > 1.5. The 4-km-long segment of the Clamshell-Sawpit fault that may have ruptured in the mainshock is outlined by several thrust focal mechanisms with an east-northeast-striking fault plane dipping to the north. To the west, several thrust aftershocks with east-striking nodal planes suggest some complexity in the aftershock faulting, such as a curved rupture surface. In addition, several strike-slip and normal faulting events occurred along the edges of the mainshock fault plane, indicating secondary tear faulting. The tectonic stress field driving the coexisting left-lateral strike-slip and thrust faults in the northern Los Angeles basin is north-south horizontal compression with vertical intermediate or minimum principal stress axis.

scholarly journals Stress-Drop and Source Scaling of the 2019 Ridgecrest, California, Earthquake Sequence

2020 ◽  
Vol 110 (4) ◽  
pp. 1859-1871 ◽  
Author(s):  
Daniel T. Trugman
Keyword(s):  
Stress Drop ◽  
Aftershock Sequence ◽  
P Wave ◽  
Earthquake Sequence ◽  
Study Region ◽  
Decomposition Approach ◽  
Trade Offs ◽  
Stress Changes ◽  
Source Scaling ◽  
Stress Drops

ABSTRACT Stress drop, while difficult to measure reliably and at scale, is a key source parameter for understanding the earthquake rupture process and its relationship to strong ground motion. Here, we use a P-wave spectral decomposition approach, designed for large and densely sampled datasets, to measure earthquake stress drop in the region surrounding the 2019 Ridgecrest, California, earthquake sequence. With more than 11,000 measurements of earthquake stress drop in the 20-yr time period from 2000 through 2019, this dataset provides an opportunity to understand how coseismic stress changes and how other geophysical factors relate to the distribution of stress drop and its evolution in space and time. We observe a mild but persistent deviation from self-similar scaling, with larger events having systematically higher stress drops, though this trend depends on the assumption of an omega-square source spectral model. Earthquake stress drop increases with hypocentral depth in this study region, and the Ridgecrest aftershocks tend to have higher stress drops than the pre-event seismicity. This is in part due to their deeper hypocenters. Coherent spatial patterns of stress drop in the aftershock sequence correlate with the slip distribution of the M 7.1 mainshock, whose northwest rupture tip terminated in a long-lived zone of enervated stress drop. Although physical interpretation of these results is complicated by the trade-offs between the timing, depth, and location of these earthquakes, the observations provide new insight into the physics of the earthquake source in an area of renewed seismic activity in southern California.

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.

scholarly journals Main shock and aftershocks of the December 13, 1990, Eastern Sicily earthquake

1995 ◽  
Vol 38 (2) ◽  
Author(s):  
A. Amato ◽  
R. Azzara ◽  
A. Basili ◽  
C. Chiarabba ◽  
M. Cocco ◽  
...  
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
Source Parameters ◽  
Source Region ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Local Network ◽  
Fault Plane Solution ◽  
Slip Mechanism ◽  
Plane Solution

n this paper we describe the location and the fault plane solution of the December 13, 1990, Eastern Sicily earthquake (ML = 5.4), and of its aftershock sequence. Because the main shock location is not well constrained due to the geometry of the permanent National Seismic Network in this area, we used a "master event" algorithm to locate it in relation to a well located aftershock. The revised location is slightly offshore Eastern Sicily, 4.8 km north of the largest aftershock (ML = 4.6) that occurred on December 16, 1990. The main shock has a strike-slip mechanism, indicating SE-NW compression with either left lateral motion on a NS plane, or right lateral on an EW plane. Two days after the main event we deployed a local network of eight digital stations, that provided accurate locations of the aftershocks, and the estimate of source parameters for the strongest earthquake. We observed an unusual quiescence after the ML = 5.4 event, that lasted until December 16, when a ML = 4.6 earthquake occurred. The fault plane solution of this aftershock shows normal faulting on E-W trending planes. Between December 16 and January 6, 1991, a sequence of at least 300 aftershock" was recorded by the local network. The well located earthquakes define a small source region of approximately 5 x 2 x 5 km3, with hypocentral depths ranging between 15 and 20 km. The paucity of large aftershocks, the time gap between the main shock occurrence and the beginning of the aftershock sequence (3.5 days), their different focal mechanisms (strike-slip vs. normal), and the different stress drop between main shock and after- shock suggest that the ML = 5.4 earthquake is an isolated event. The sequence of aftershocks began with the ML = 4.6 event, which is probably linked to the main shock with a complex mechanism of stress redistribution after the main faulting episode.

scholarly journals Static stress drop in the 1994 Northridge, California, aftershock sequence

1997 ◽  
Vol 87 (6) ◽  
pp. 1495-1501
Author(s):  
Jeanne L. Hardebeck ◽  
Egill Hauksson
Keyword(s):  
Stress Drop ◽  
Measurement Errors ◽  
Aftershock Sequence ◽  
Static Stress ◽  
Lower Stress ◽  
High Frequencies ◽  
Order Of Magnitude ◽  
Confining Pressures ◽  
Static Stress Drop ◽  
Stress Drops

Abstract We use time-domain pulse widths to estimate static stress drops for 279 ML 2.5 to 4.0 aftershocks of the 17 January 1994, MW 6.7 Northridge, California, earthquake. The stress drops obtained range from 0.02 to 40 bars, with a log average of 0.75 bar. Error bars computed for our estimates are typically a factor of 5, indicating that the three order of magnitude scatter in stress drops is not solely a result of measurement errors and that there is a significant amount of heterogeneity in the static stress drops of the aftershocks. Stress drops might be expected to increase with depth, since a fault can maintain a higher shear load at higher confining pressures. We observe an increase in log average stress drop at about 15 km depth, which is statistically significant at the 80% confidence level. The increase is due primarily to a lack of lower stress-drop events below this depth and may be controlled by material properties since the Northridge aftershocks are observed to intersect an anomalously high-velocity body at around this depth (Hauksson and Haase, 1997). An apparent increase in stress drop with magnitude is also observed over the entire magnitude range of the study, although whether this trend is real or an artifact of attenuation of high frequencies in the upper crust is unresolved.

The 2017 November 12 Mw 7.3 Sarpol-Zahab (Iran-Iraq border region) earthquake: source model, aftershock sequence and earthquakes triggering

2020 ◽  
Author(s):  
Mohammadreza Jamalreyhani ◽  
Mehdi Rezapour ◽  
Simone Cesca ◽  
Sebastian Heimann ◽  
Hannes Vasyura-Bathke ◽  
...  
Keyword(s):  
Fault Plane ◽  
Joint Inversion ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Fault Slip ◽  
Earthquake Source ◽  
Border Region ◽  
Model Parameters ◽  
Fault Geometry ◽  
Large Earthquakes

<p>The Mw 7.3 Sarpol-Zahab earthquake occurred on 12 November 2017 in the Lurestan arc of the Zagros Simply Folded Belt (ZSFB). It is estimated that 600 people were killed and 8000 were injured in this earthquake. This earthquake has been the largest instrumentally recorded earthquake in the ZSFB and its moment, as well as its mechanism, were unexpected. We present an earthquake source study on the Mw 7.3 Sarpol-Zahab earthquake, two large following earthquakes in the region in 2018 and their corresponding aftershock sequences to gain insight of seismotectonic of the Lurestan arc fold-thrust belt.</p><p>In this study, we complement previous studies on this earthquake, by non-linear probabilistic optimization of joined geodetic and seismic data using a new, efficient Bayesian bootstrap-based optimization scheme to infer the finite fault geometry and fault slip together with meaningful uncertainty estimates of the model parameters. Our optimization is based on the modeling of ascending and descending Sentinel-1 satellite data, seismological waveform from global seismic networks and the strong motion network of Iran. The posterior mean model of the Sarpol-Zahab earthquake shows that the causative fault plane is centered at is 14±2 km depth and has a low dip angle of 17°±2° and a strike of 350°±10°. The rake angle of 144°±4° points to an oblique thrust mechanism. The rupture area of the uniform-slip, rectangular model is 40±2 km long and 16±2 km width and shows 4.0±0.5 m fault slip, which results in a magnitude estimate of Mw 7.3±0.1.</p><p>Later, in August and November 2018, two large earthquakes with Mw 6.0 and Mw 6.4 occurred about 40 km east and 60 km south of the Sarpol-Zahab epicenter, respectively. These earthquakes could have been triggered by the 2017 Sarpol-Zahab earthquake. We apply the same joint inversion modeling to derive the corresponding fault plane solutions. We found strike-slip mechanisms for both events but centroid depths at 10±2 km and 16±2 km for Mw 6.0 and Mw 6.4, respectively.</p><p>The 2017 Sarpol-Zahab earthquake and the following studied 2018 earthquakes were followed by a sustained aftershock sequence, with more than 133 aftershocks exceeding Ml 4.0 until December 30, 2019. We rely on the local and regional seismic broad-band stations of Iran and Iraq permanent networks to estimate full-waveform moment tensor solutions of 70 aftershocks down to Ml 4. Most of these aftershocks have shallow centroid depths between 5 and 12 km, so that they occurred in the uppermost part of the basement and/or in the lower sedimentary cover, which is ~8 km thick in this area.</p><p>Our results suggest that the Sarpol-Zahab earthquakes activated low-angle thrust faults and shallower strike-slip structures, highlighting that both thin- and thick-skin deformation take place in the fold-thrust belts in the Lurestan arc of the Zagros. Such information on the deformation characteristics is important for the hazard and risk assessment of future large earthquakes in this region.<br>Additionally, we demonstrate how the joint inversion of different geophysical data can help to better resolve the fault geometry and the earthquake source parameters.</p>

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.

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