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>

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 Development of an inversion method to extract information on fault geometry from teleseismic data

2019 ◽  
Vol 220 (2) ◽  
pp. 1055-1065 ◽  
Author(s):  
Kousuke Shimizu ◽  
Yuji Yagi ◽  
Ryo Okuwaki ◽  
Yukitoshi Fukahata
Keyword(s):  
Fault Plane ◽  
Slip Rate ◽  
Rate Function ◽  
Fault Slip ◽  
Body Waves ◽  
Fault System ◽  
Inversion Method ◽  
Fault Geometry ◽  
Finite Fault ◽  
Extract Information

SUMMARY Teleseismic waveforms contain information on fault slip evolution during an earthquake, as well as on the fault geometry. A linear finite-fault inversion method is a tool for solving the slip-rate function distribution under an assumption of fault geometry as a single or multiple-fault-plane model. An inappropriate assumption of fault geometry would tend to distort the solution due to Green’s function modelling errors. We developed a new inversion method to extract information on fault geometry along with the slip-rate function from observed teleseismic waveforms. In this method, as in most previous studies, we assumed a flat fault plane, but we allowed arbitrary directions of slip not necessarily parallel to the assumed fault plane. More precisely, the method represents fault slip on the assumed fault by the superposition of five basis components of potency-density tensor, which can express arbitrary fault slip that occurs underground. We tested the developed method by applying it to real teleseismic P waveforms of the MW 7.7 2013 Balochistan, Pakistan, earthquake, which is thought to have occurred along a curved fault system. The obtained spatiotemporal distribution of potency-density tensors showed that the focal mechanism at each source knot was dominated by a strike-slip component with successive strike angle rotation from 205° to 240° as the rupture propagated unilaterally towards the south-west from the epicentre. This result is consistent with Earth’s surface deformation observed in optical satellite images. The success of the developed method is attributable to the fact that teleseismic body waves are not very sensitive to the spatial location of fault slip, whereas they are very sensitive to the direction of fault slip. The method may be a powerful tool to extract information on fault geometry along with the slip-rate function without requiring detailed assumptions about fault geometry.

The Mw 5.8 Mineral, Virginia, Earthquake of August 2011 and Aftershock Sequence: Constraints on Earthquake Source Parameters and Fault Geometry

2013 ◽  
Vol 104 (1) ◽  
pp. 40-54 ◽  
Author(s):  
D. E. McNamara ◽  
H. M. Benz ◽  
R. B. Herrmann ◽  
E. A. Bergman ◽  
P. Earle ◽  
...  
Keyword(s):  
Source Parameters ◽  
Aftershock Sequence ◽  
Earthquake Source ◽  
Fault Geometry ◽  
Earthquake Source Parameters ◽  
Virginia Earthquake ◽  
Sequence Constraints

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.

Operational Aftershock Forecasting for 2017-2018 Seismic Sequence in Western Iran

2021 ◽  
Author(s):  
Fatemeh Jalayer ◽  
Hossein Ebrahimian
Keyword(s):  
Model Updating ◽  
Aftershock Sequence ◽  
Border Region ◽  
Model Parameters ◽  
Time Interval ◽  
Seismic Sequence ◽  
Epicentral Area ◽  
Western Iran ◽  
Spatio Temporal ◽  
Robust Reliability

<p>On Sunday November 12, 2017, at 18:18:16 UTC, (21:48:16 local time), a strong earthquake with Mw7.3 occurred in western Iran in the border region between Iran and Iraq in vicinity of the Sarpol-e Zahab town. Unfortunately, this catastrophic seismic event caused 572 causalities, thousands of injured and vast amounts of damage to the buildings, houses and infrastructures in the epicentral area. The mainshock of this seismic sequence was felt in the entire western and central provinces of Iran and surrounding areas. The main event was preceded by a foreshock with magnitude 4.5 about 43 minutes before the mainshock that warned the local residence to leave their home and possibly reduced the number of human casualties. More than 2500 aftershocks with magnitude greater than 2.5 have been reported up to January 2019 with the largest registered aftershock of Mw6.4. A novel and fully-probabilistic procedure is adopted for providing spatio-temporal predictions of aftershock occurrence in a prescribed forecasting time interval (in the order of hours or days). The procedure aims at exploiting the information provided by the ongoing seismic sequence in quasi-real time. The versatility of the Bayesian inference is exploited to adaptively update the forecasts based on the incoming information as it becomes available. The aftershock clustering in space and time is modelled based on an Epidemic Type Aftershock Sequence (ETAS). One of the main novelties of the proposed procedure is that it considers the uncertainties in the aftershock occurrence model and its model parameters. This is done by moving within a framework of robust reliability assessment which enables the treatment of uncertainties in an integrated manner. Pairing up the Bayesian robust reliability framework and the suitable simulation schemes (Markov Chain Monte Carlo Simulation) provides the possibility of performing the whole forecasting procedure with minimum (or no) need of human interference. The fully simulation-based procedure is examined for both Bayesian model updating of ETAS spatio-temporal model and robust operational forecasting of the number of events of interest expected to happen in various time intervals after main events within the sequence. The seismicity is predicted within a confidence interval from the mean estimate.</p>

Seismological Constraints on Fault-Slip Source Models and Rupture Characteristics of Global Large Earthquakes (Mw ≥ 7.5) and Associated Tsunamis

2020 ◽  
Author(s):  
Seda Yolsal-Çevikbilen ◽  
Tuncay Taymaz
Keyword(s):  
Near Field ◽  
Fault Slip ◽  
Earthquake Source ◽  
P Wave ◽  
Slip Distribution ◽  
Distribution Models ◽  
Tsunami Waves ◽  
Source Mechanisms ◽  
Source Models ◽  
Large Earthquakes

<p>Large and destructive earthquakes (M<sub>w</sub>≥ 7.5) occur worldwide particularly along the major subduction zones causing extensive damage and loss of life in the hinterland of epicentral region. Source models and rupture characteristics of these earthquakes (i.e. faulting geometry, focal depth, non-uniform finite-fault slip distributions) can be precisely determined by using seismological data and multidisciplinary earth-science observations. It is also known that earthquake source parameters play key roles in the modelling of secondary events such as earthquake-induced tsunamis. There are many studies emphasizing the importance of using heterogonous slip distribution models of earthquakes in mathematical tsunami simulations to predict synthetic tsunami waves more consistent with the observed ones. In this study, we obtained double-couple source mechanisms and slip distribution models of complex large earthquakes (M<sub>w</sub>≥ 7.5) lately occurred at different parts of the Earth. For this purpose, we used point-source teleseismic P- and SH- body waveform inversion and kinematic slip distribution inversion techniques. Besides, azimuthal distributions of P- wave first motion polarities, which are recorded by near-field and regional seismic stations, are checked to approve obtained minimum misfit source mechanism parameters of earthquakes. We essentially observed that tsunamigenic earthquakes occurred at shallow focal depths (h ≤ 70 km) with dip-slip source mechanisms and rather complex slip distributions along the fault planes. However, in some cases, tsunami waves may be unexpectedly triggered due to the secondary effects of large strike-slip earthquakes (e.g., September 28, 2018 Palu, Indonesia - M<sub>w</sub>7.5). Here, we discuss our inversion results, which reveal the significant contributions of earthquake source studies on resolving the relationships between the faulting geometry, rupture characteristics and tsunami generation. Furthermore, the necessity of high-resolution bathymetry data in numerical tsunami simulations is highlighted for the modelling of tsunami waves, in particular, recorded at the near-field tide-gauge stations. This study is partially supported by the Turkish Academy of Sciences (TÜBA) through GEBIP program.</p>

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 Normal Faulting Movement During the 2020 Mw 6.4 Yutian Earthquake: A Shallow Rupture in NW Tibet Revealed by Geodetic Measurements

2020 ◽  
Author(s):  
Jiansheng Yu ◽  
Dongzhen Wang ◽  
Bin Zhao ◽  
Li Qi
Keyword(s):  
Strike Slip ◽  
Model Parameters ◽  
Fault Geometry ◽  
Normal Faulting ◽  
Geometry Model ◽  
Radar Images ◽  
The North ◽  
Altyn Tagh ◽  
Finite Fault ◽  
Stress Changes

Abstract The ENE striking Longmu Co fault and the North Altyn Tagh left-lateral slip fault have led to the complex regional structure in the northwestern Tibetan Plateau, resulting in a series of normal faulting and strike slip faulting earthquakes. Using both the ascending and descending Sentinel-1A/B radar images, we depict the coseismic deformation caused by the 2020 Yutian Mw 6.4 earthquake with a peak subsidence of ~20 cm. We determine the seismogenic fault geometry by applying the Bayesian approach with a Markov Chain Monte Carlo sampling method, which enables us to find the posterior probability density functions of the source model parameters. The estimation results reveal that the earthquake have dominantly by normal slip with moderate strike slip component. Based on the optimal fault geometry model, we extend the fault plane and invert for the finite fault model dislocation, which indicate that the slip is mainly concentrated at a shallow focal depth of 3–10 km with a maximum slip of ~1.0 m. Our preferred geodetic coseismic model exhibits no surface rupture, which may likely due to the shallow slip deficit in the uppermost crust. We calculate the combined loading effect of the Coulomb failure stress changes induced by the coseismic dislocations and postseismic viscoelastic relaxation of the 2008 Mw 7.1 and 2014 Mw 6.9 Yutian events. Our study demonstrates that the two preceding major Yutian shocks were insufficient to trigger the 2020 Yutian earthquake, which we consider perhaps reflects the natural release of elastic strain accumulated mainly through localized tectonic movement. We attribute the 2020 Yutian event to the release of extensional stress in a stepover zone controlled by the Longmu Co and the North Altyn Tagh sinistral strike slip fault systems. The seismic risk in the southwest end of the North Altyn Tagh fault has been elevated by the Yutian earthquake sequences, which require future attention.

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.

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