Slip Area Research Articles

The 12 November 2017 Mw 7.3 Ezgeleh‐Sarpolzahab (Iran) Earthquake and Active Tectonics of the Lurestan Arc

AbstractThe 12 November 2017 Mw 7.3 Ezgeleh‐Sarpolzahab earthquake is the largest instrumentally recorded earthquake in the Zagros Simply Folded Belt by a factor of ∼10 in seismic moment. Exploiting local, regional, and teleseismic data and synthetic aperture radar interferometry imagery, we characterize the rupture, its aftershock sequence, background seismicity, and regional tectonics. The mainshock ruptured slowly (∼2 km/s), unilaterally southward, for ∼40 km along an oblique (dextral‐thrust) fault that dips ∼14°E beneath the northwestern Lurestan arc. Slip is confined to basement depths of ∼12–18 km, resolvably beneath the sedimentary cover which is ∼8 km thick in this area. The gentle dip angle and basement location allow for a broad slip area, explaining the large magnitude relative to earthquakes in the main Fars arc of the Zagros, where shallower, steeper faults are limited in rupture extent by weak sedimentary layers. Early aftershocks concentrate around the southern and western edges of the mainshock slip area and therefore cluster in the direction of rupture propagation, implying a contribution from dynamic triggering. A cluster of events ∼100 km to the south near Mandali (Iraq) reactivated the ∼50° dipping Zagros Foredeep Fault. The basement fault responsible for the Ezgeleh‐Sarpolzahab earthquake probably accounts for the ∼1 km elevation contrast between the Lurestan arc and the Kirkuk embayment but is distinct from sections of the Mountain Front Fault that define frontal escarpments elsewhere in the Zagros. It may be related to a seismic interface underlying the central and southern Lurestan arc, and a key concern is whether or not the more extensive regional structure is also seismogenic.

Fracture failure analysis and research on slip of casing head

Abstract In this paper, macro and micro analysis is made on the slip of casing head which is fractured in situ. Visual inspection and microscopic analysis of fracture surface shows that the feature of crack is intergranular brittle fracture. The final crack originates from the root of the slip tooth and extends along the longitudinal, radial and circumferential directions. Because the initial crack is closer to the end of the slip, the longitudinal crack first reaches the end and then complete fracture is caused. The metallographic analysis shows that the microstructure of material has not been completely transformed into a sorbite, indicating that there is a defect in the heat treatment process. The minimum average impact energy of three samples is close to the minimum requirement, which shows the brittleness of material increases and the impact toughness decreases a lot at −29 °C. The finite element analysis shows that the high stress is mainly distributed in the shoulder area of slip, with the maximum stress being 875.5 MPa, which exceeds the allowable yield strength of the material. To ensure the safety of wellhead, the split-type slip can be used to reduce the stress concentration of slip. These test results provide powerful guidance for design, material selection and maintenance of slip to effectively reduce the accident in the process of oil and gas development.

Experimental Investigation into the Bedding Plane Slip Effect on the Overlying Strata Behavior in Longwall Top Coal Caving of Soft Coal Seam

Bedding plane shear slip becomes more obvious in rock strata with quite different mechanical properties. A composite beam model considering the behaviors of the main roof and the immediate roof in the “three‐soft” coal seam is established based on physical similarity simulation experiments and the slip theory in this paper. The movement and failure of the overlying strata and the mechanism of the bedding plane slip at the 2211 working face are studied by experimental and theoretical analysis. The results suggest that the front abutment stress distribution occurs 50 m ahead of the working face, the initial caving interval of the main roof is 55 m, and the peak stress appears at a distance 20 to 32 m ahead of the working face. The bedding plane slip areas can be divided into the obvious slip area and the slight slip area along the mining direction. The range of the obvious slip area becomes wider and the range of the slight slip area grows to be narrower as the working face advances. The bedding plane slip becomes steady after gradual increase and leads to the subsidence of the overlying strata in the “three‐soft” coal seam. The observed initial caving interval of the main roof by field measurement is 51 m, which is consistent with the results of physical similarity simulation experiments and theoretical analysis. The results demonstrate that the beam slip model proposed in this paper is reasonable and able to describe the behaviors of overlying strata and bedding plane slip.

ПРОБЛЕМЫ СЦЕПЛЕНИЯ АРМАТУРЫ ПЕРИОДИЧЕСКОГО ПРОФИЛЯ С БЕТОНОМ

Introduction: Based on an analysis of issues related to the anchorage and active adhesion between deformed reinforcement and concrete, it is possible to identify major problems of concrete-to-steel bond breaking during the operation of bearing building structures. Purpose of the study: The authors seek to determine the mechanism of interaction between concrete and steel in the adhesion contact area, establish a relationship between external force action and crack development in the contact area. Methods: The authors suggest some dependencies to evaluate various test methods when determining the area where two materials, differing in physical characteristics, interact. Approximation to the actual phenomena related to the interaction between concrete and reinforcement, starting from the moment when through and non-through internal cracks form in the contact area and ending with destruction, is a general problem of models describing the adhesion of materials. Results: The theoretical results were compared with the experimental data and recommendations of modern regulatory documents, and it was found that they are in a satisfactory agreement. It was established that the difference of axial deformations of the bar and the surrounding concrete goes into the difference of bending displacements, which explains uneven load distribution across the protrusions. Discussion: Using the suggested dependencies, it is possible to predict crack development in the contact area of the reinforcement and cement binder as well as in the slip area in an extreme case. The concrete tensile strength in particular reinforcedconcrete elements in supporting cross-sections and with anchorage in tensile concrete represents a factor affecting the strength of the concrete-to-steel bond.

Spatio-temporal changes in the seismic velocity induced by the 2011 Tohoku-Oki earthquake and slow slip event revealed from seismic interferometry, using ocean bottom seismometer\u2019s records

Seismic interferometry is one of the most effective techniques for detecting temporal variations in seismic velocity caused by large earthquakes. Before the 2011 Tohoku-Oki earthquake (Mw9.0) near the Japan Trench, a slow slip event (SSE, Mw7.0) and low-frequency tremors were observed near the trench. Here, we applied a seismic interferometry technique using ambient noise to data from 17 ocean bottom seismometers (OBSs) installed above the focal region before the main shock. We used our technique to detect temporal variations in seismic velocity caused by the main shock, SSE, and low-frequency tremors. In the region above the large coseismic slip area, we detected a 1–2% seismic velocity decrease after the main shock. In addition, we observed very small temporal increases in seismic velocity near the SSE fault during the initial SSE stage. Moreover, for most of the OBSs, we observed temporal variations in the autocorrelation functions (ACFs) during the low-frequency tremors. These may have been caused by temporal variations in the ambient noise source distributions, resulting from low-frequency tremors. These results suggest the possibility of detecting low-frequency tremors using ACF monitoring.

438. Finding Toxocara Eggs in Park Soil From Montgomery County, Pennsylvania

Background Toxocara canis (dogs) and Toxocara cati (cats) is a parasitic worm commonly called roundworm. Toxocara eggs are spherical to oblong in shape, have a rough/pitted edge, appear brownish in color, and measures 75–90 µm (T. canis) and 65–70 µm (T. cati). This environmental surveillance study was designed to examine Toxocara contamination levels of selected parks in Montgomery County, Pennsylvania for the first time.MethodsSix soil samples (2 cups each) were obtained from six different parks, for a total of 36 samples. Two table spoons of dried/sifted soil were added to a glass, covered with 1/4 cup of a sugar floatation solution, stirred for 30 seconds, and let sit for 1 hour. The supernatant was transferred to a 20 mL plastic tube, capped, and let sit overnight. Three drops of surface fluid were placed on a glass slide and examined at ×400 total magnification. The number of Toxocara eggs from a full grid search of the cover slip area was recorded.ResultsOverall, 35 of 36 samples tested positive for Toxocara eggs. The parks and samples varied in their levels of contamination of Toxocara eggs; smallest samples (0 and 2 eggs) from Sanatoga Park and largest samples from Pottstown Memorial Park [52 eggs – picnic pavilion] and Heather Place Park [56 eggs – tree grove]. The average number of eggs from Sanatoga Park (2.5 eggs [95% CI: 1.0, 4.0]), Gerald Richards Park (4.0 eggs [95% CI: 3.8, 6.2]), and Althouse Arboretum (4.7 eggs [95% CI: 3.3, 6.1]) were significantly lower than Manderach Park (11.7 eggs [95% CI: 9.6, 13.8]). Sanatoga, Gerald Richards, and Heather Place had similar average number of eggs (χ2 = 3.97 < 5.99). Pottstown Memorial Park (18.2 eggs [95% CI: 4.1, 32.1]) and Heather Place Park (18.5 eggs [95% CI: 3.5, 23.5]) had the highest averages; both parks had very similar average number of eggs (χ2 = 0.02 < 3.84).ConclusionThis study demonstrated that Toxocara eggs could be found in every park that was tested. The number of eggs per sampled varied greatly; highest amounts in areas that could contain food droppings (e.g., picnic area) or potential bathrooms for dogs (e.g., tree grove). Some parks were significantly less infected with an average number of Toxocara eggs than other parks.Disclosures All authors: No reported disclosures.

Teleseismic finite-fault inversion of two Mw = 6.4 earthquakes along the East Anatolian Fault Zone in Turkey: the 1998 Adana and 2003 Bingöl earthquakes

The East Anatolian Fault Zone is a continental transform fault accommodating westward motion of the Anatolian fault. This study aims to investigate the source properties of two moderately large and damaging earthquakes which occurred along the transform fault in the last two decades using the teleseismic broadband P and SH body waveforms. The first earthquake, the 27 June 1998 Adana earthquake, occurred beneath the Adana basin, located close to the eastern extreme of Turkey’s Mediterranean coast. The faulting associated with the 1998 Adana earthquake is unilateral to the NE and confined to depths below 15 km with a length of 30 km along the strike (53°) and a dipping of 81° SE. The fixed-rake models fit the data less well than the variable-rake model. The main slip area centered at depth of about 27 km and to the NE of the hypocenter, covering a circular area of 10 km in diameter with a peak slip of about 60 cm. The slip model yields a seismic moment of 3.5 × 1018 N-m (Mw ≅ 6.4). The second earthquake, the 1 May 2003 Bingol earthquake, occurred along a dextral conjugate fault of the East Anatolian Fault Zone. The preferred slip model with a seismic moment of 4.1 × 1018 N-m (Mw ≅ 6.4) suggests that the rupture was unilateral toward SE and was controlled by a failure of large asperity roughly circular in shape and centered at a depth of 5 km with peak displacement of about 55 cm. Our results suggest that the 1998 Adana earthquake did not occur on the mapped Goksun Yakapinar Fault Zone but rather on a SE dipping unmapped fault that may be a split fault of it and buried under the thick (about 6 km) deposits of the Adana basin. For the 2003 Bingol earthquake, the final slip model requires a rupture plane having 15° different strike than the most possible mapped fault.

Formation and characteristics of Guang’an Village landslide in Wuxi, Chongqing, China

At 00:20 on 21 October 2017, a large landslide occurred in Guang’an Village, Wuxi County, Chongqing, China. The overall length of the landslide was approximately 1500 m, the width was approximately 1300 m, the distribution area was approximately 1.95 km2, and the total volume was approximately 24.8 million m3, with volume of the slipped area being approximately 6 million m3. Nine people were reported missing after the landslide deposits accumulated in the riverbed of the Xixi River and blocked approximately 160 m of the river, forming a dammed lake. We investigated the cause and mechanism of the initiation and development of the landslide using field investigations and on-site monitoring. The formation process of landslides can be divided into three stages: the start-up stage of the rock avalanche, the transportation stage, and the accumulation stage. In this case, the strength of the upper limestone was much greater than the strength of the lower shale. Under the effect of groundwater softening, the lower shale was plastically deformed with the combination of weak and hard lithologies, resulting in a rapid slip of the upper rock mass under gravity. After the slip of the rock mass in the source area, the rock mass of the lower slope was pushed downward. Then, the sliding mass moved from the source area pushing through the transportation area and formed the depositional area. There is still a possibility of further slip, so preventive measures must be taken as soon as possible to manage the potential slippage.

The Contact Mechanics of Novikov’s Surface-Hardened Gearing during Running-in Process

The article is devoted to the analysis of the state of the contact surfaces of the higher kinematic pair in the general case of relative motion, that is, in the presence of rolling, sliding, and twisting, which is characteristic of Novikov’s circular-screw gears. The purpose of the work is to assess the impact of friction forces, the state of contact surfaces after tool processing, and the localization of the instantaneous contact spot on the level of contact—fatigue durability of gears. Power contact in the presence of geometric slippage of the mating surfaces leads to a significant change in the initial geometry and the mechanical properties of surface layers. In the existing methods of calculations of contact strength, the effect of running-in is investigated insufficiently, which leads to an incorrect result, especially for gear with high hardness of the teeth. In this work, the conditions of contact interaction close to the real requirements are studied on the basis of experimental material, numerical solution of the contact problem, determination of the terms of the contact areas of slip, and adhesion within the instantaneous spot. The shape of the instant contact spot has asymmetry and can be approximated by an ellipse with the introduction of a correction factor. The running-in period is of a plastic nature with cold deformation and reduction of the roughness of surfaces. As a result of the run-in period, the area of actual contact (tooth height) is increased by 2 or more times. It is not desirable to spread the area of contact at the area of adhesion that initiates the formation of pitting. The presence of defective surface area on the level of contact strength does not have significant influence, because of the running-in period, but increases the risk of spalling and brittle fracture.

Theoretical calculation of the instantaneous friction-induced energy losses in arbitrarily excited axisymmetric mechanical contact systems

In this paper, we present the theoretical formula for calculating a friction-induced energy loss in a mechanical contact system consisting of two convex axisymmetric bodies subject to arbitrarily varying oblique loading. Non-flat contact geometry engenders a particular regime, partial slip, in which weakly compressed areas of the contact zone slip, while strongly compressed ones stick. Mechanical energy is transformed into heat only in the slip area in which two field characteristics should be calculated: the local infinitesimal slip distance distribution and shear stress. Their product equals the spatial distribution of the energy loss or heat source density, while the integration over the slip zone produces the global energy loss. The energetic characteristics are obtained in a general situation. In the proposed method, energy losses can be calculated at any time during a loading protocol, in the general case of an arbitrary load expressed in terms of normal and tangential displacements. This is a step forward in comparison to more traditional approaches in contact mechanics allowing to calculate the energy loss per period in the case where the contact is excited by a single periodic input. In this work, the loading is limited to two dimensions: one normal and one tangential. Therefore, the tangential loading is colinear with the tangential displacement. All required contact characteristics, including displacement and stress distributions, are provided by the semi-analytical Method of Memory Diagrams (MMD) that has initially been developed to obtain memory-dependent solutions to the problem of frictional contact between axisymmetric profiles and has later been generalized for rough surfaces. Correspondingly, the proposed solution is exact for axisymmetric bodies and is approximately valid in the case of rough surfaces for which the energy loss per unit nominal area is calculated. The obtained theoretical results for energy dissipation are compared to analytical and numerical calculations for periodic and non-periodic loading situations, illustrating the potential of this method in realistic contact settings.

Evolution and Distribution of the Early Aftershocks Following the 2008 Mw 7.9 Wenchuan Earthquake in Sichuan, China

AbstractUsing seismic data recorded by a dense temporary seismic array, we apply a waveform matched‐filter technique and obtain an early aftershock catalog around the mainshock rupture zone of the 2008 Wenchuan, Sichuan, China, earthquake. Specifically, we use 1,273 events in a relocated aftershock catalog as templates and scan through the waveforms within 7 days following the mainshock. We obtain up to ∼5.3 and ∼10 times more aftershocks than the standard and relocated catalogs, respectively. We find that early aftershocks mostly occurred below 10 km depth, downdip to large coseismic slip areas. Early aftershocks also show minor along‐strike migration with time since the mainshock, indicating triggering of afterslip following the mainshock. From the epicentral region to Beichuan where the mainshock slip was primarily reverse faulting, early aftershocks illustrated the Yingxiu‐Beichuan and Guanxian‐Jiangyou faults as high‐angle listric feature and rooted to a gentle dipping plane at the depth of ∼20 km. The aftershocks in the northeast segment of the Longmen Shan faults mostly occurred along a near‐vertical dipping fault, consistent with the primary strike‐slip component of mainshock slip in this region. In addition, differences in early and long‐term aftershock distribution indicate significant postseismic deformation along the conjugate Xiaoyudong fault. Our results help to illuminate the deep geometry of the Longmen Shan fault zone and the early evolution after the Wenchuan mainshock, which provides additional constraints to the mechanism of plateau uplifting.

Extremely early recurrence of intraplate fault rupture following the Tohoku-Oki earthquake

Intraplate earthquakes on a fault in Earth’s upper crust commonly recur in 1,000 years or longer. The 2011 M9 Tohoku-Oki earthquake triggered the activation of intraplate earthquakes in northern Kanto, Japan, including two M6 events on 19 March 2011 and 28 December 2016 located near one another. Here we use displacements captured by satellite radar and the Global Navigation Satellite System to show that the two earthquakes ruptured an identical fault. Detailed fault slip modelling shows that the deformation data for the two earthquakes are well explained by slip along a common fault geometry, and that the majority of the slipped area on the fault overlaps. Strain analysis reveals that the first M6 earthquake was followed by exceptionally large postseismic deformation. Such deformation is consistent with afterslip around the M6 rupture area, which in turn rebuilds the shear stress on the fault enabling the next earthquake. We infer that the rapid and large postseismic deformation of the 2011 Tohoku-Oki earthquake promoted such afterslip and made the second earthquake recur in just 5.8 years. This study suggests a mechanism to explain observations of extreme temporal clustering in palaeoseismic earthquake recurrence studies. A pair of closely spaced intraplate earthquakes in Japan can be explained by postseismic deformation associated with the 2011 Tohoku-Oki earthquake.

Mainshocks/aftershocks study of the August 2012 earthquake doublet on Ahar-Varzaghan complex fault system (NW Iran)

Seismotectonic features of the Ahar-Varzaghan complex fault system are reviewed by the mainshocks/aftershocks study of the 2012 Ahar-Varzaghan earthquake doublet (Mw = 6.5 & Mw = 6.3). The early aftershocks were accurately monitored by a dense local seismological network. The mainshocks hypocenters were relocated using a new velocity model for the area. The regional displacement waveforms of the mainshocks and large aftershocks were jointly inverted for their moment tensors and centroids.Precisely located aftershocks are mostly distributed in three distinct clusters. These E-W trending clusters are situated to the north of the surface rupture over a ∼30 km long and 10 km wide zone, extending from the ground surface down to the depth of ∼15 km. Based on our results, the first mainshock (M1) with Mw = 6.5 nucleated 3 km east of the surface rupture at a depth of 10 km. The rupture evolved toward the west and shallower depths on an almost E-W striking right-lateral strike-slip vertical fault plane and produced ∼12 km surface rupture. Its main energy was released at about 5 km west of the hypocenter at an average depth of 5 km. About 11 min later, the second mainshock (M2) with Mw = 6.3 nucleated 5 km northwest of the M1 hypocenter and at a depth of 15 km. It occurred on an ENE-WSW striking, north-dipping (65° to 70°) fault plane with a dominant reverse mechanism and strike-slip component. The M2 related rupture also expanded to the west and to shallower depths and released most of its energy ∼5 km west of the respective hypocenter at an average depth of 11 km. The eastern aftershocks mainly show the right-lateral strike-slip mechanism on almost E-W trending fault, close to the location of the first main centroid (M1). The northern aftershocks mostly include reverse mechanisms with strike-slip component near the M2 centroid. A big gap of aftershock activity is observed close to the M1 centroid location, most likely associated with the area of maximum slip. We do not observe any N-S lineament of aftershocks neither near the M2 hypocenter and nor its centroid, thus making the suggestion of some previous investigators that M2 ruptured an N-S trending fault unlikely.

Stochastic Source Model for Strong Motion Prediction

The article aims at developing a stochastic model which simulates spatial distribution of slip on the fault plane. This is achieved by analysing a large dataset of 303 finite-fault rupture models from 152 past earthquakes with varying fault mechanisms and in the magnitude range of 4.11-9.12. New scaling relations to predict the seismic source parameters such as fault length, fault width, rupture area, mean and standard deviation of slip have been derived for distinct fault mechanisms. The developed methodology models the spatial variability of slip as a two-dimensional von Karman power spectral density function (PSD) and correlation lengths are estimated. The proposed stochastic slip model is validated by comparing the simulated near-field ground response with the recorded data available for the 20th September 1999 Chi-Chi earthquake, Taiwan.

Why Do Aftershocks Occur Within the Rupture Area of a Large Earthquake?

AbstractThe mainshock‐aftershock sequence is one of the fundamental characteristics of seismogenesis, yet the physical mechanism of aftershock generation remains poorly understood. The simple explanation that aftershocks are caused by the mainshock's redistribution of strain energy is not always applicable, especially for aftershocks within the mainshock slip area, where strain energy is released. Here we show that the genesis of aftershocks can be modeled using a frictionally heterogeneous fault system. We conducted quasi‐dynamic numerical simulations of fault rupture cycles on a finite fault governed by a rate‐ and state‐dependent friction law. Aftershocks are observed around and within the mainshock rupture area when the frictional heterogeneity varies significantly along the fault. On the other hand, aftershocks are not produced when along‐fault variations in the frictional heterogeneity are small, which mimics the observed lack of aftershocks for repeating earthquakes.

Effect of relaxation-dependent adhesion on pre-sliding response of cartilage.

Possible links between adhesive properties and the pre-sliding (static) friction response of cartilage are not fully understood in the literature. The aims of this study are to investigate the relation between adhesion and relaxation time in articular cartilage, and the effect of relaxation-dependent adhesion on the pre-sliding response of cartilage. Adhesion tests were performed to evaluate the work of adhesion of cartilage at different relaxation times. Friction tests were conducted to identify the pre-sliding friction response of cartilage at relaxation times corresponding to adhesion tests. The pre-sliding friction response of cartilage was systematically linked to the work of adhesion and contact conditions by a slip-based failure model. It was found that the work of adhesion increases with relaxation time. Also, the work of adhesion is linearly correlated to the resistance to slip-based failure. In addition, as the work of adhesion increases, the adhered (stick) area at the moment of failure increases, and the propagation rate of the annular slip (crack) area towards its centre increases. These findings offer a mechanistic explanation of the pre-sliding friction behaviour and stick–slip response of soft hydrated interfaces such as articular cartilage and hydrogels. In addition, the linear correlation between adhesion and threshold to slip-based failure enables estimation of the adhesive strength of such interfaces directly from the pre-sliding friction response (e.g. shear wave elastography).

Repeated drainage from megathrusts during episodic slow slip

Pore-fluid pressure levels are considered to regulate the frictional strength and slip behaviour at megathrusts, where the largest earthquakes on Earth occur. Some analyses have suggested that the breaking of permeability seals during megathrust earthquakes causes subsequent drainage from the megathrust. However, it is poorly understood whether drainage follows frequent occurrences of episodic slow slip events. Here we analyse seismic waveform data beneath Kanto, Japan, for the period from 2004 to 2015 and show that seismicity rates and seismic attenuation above the megathrust of the Philippine Sea slab change cyclically in response to accelerated slow slip. These observations are interpreted to represent intensive drainage during slow slip events that repeat at intervals of approximately one year and subsequent migration of fluids into the permeable overlying plate. Our observations suggest that if slow slip events occur under an impermeable overlying plate, fluids draining due to slow slip events could be forced to channel within the megathrust, potentially enhancing pore-fluid pressure at an up-dip, locked seismogenic megathrust. This process might increase the potential to trigger large earthquakes near slow slip areas. Although stress transfer is recognized as an important factor for triggering megathrust failure, fluid transfer accompanied by episodic slow slip events will thus play an additional and crucial part in megathrust weakening. Slow slip events may cause fluids to drain from the plate boundary into the overlying plate at subduction zones, according to seismic analyses of events recorded in Kanto, Japan.

Relocation of mainshock and aftershock sequence of the &amp;lt;italic&amp;gt;M&amp;lt;/italic&amp;gt;&amp;lt;sub&amp;gt;s&amp;lt;/sub&amp;gt;7.0 Sichuan Jiuzhaigou earthquake

An earthquake of M s7.0 struck Jiuzhaigou Country in Sichuan Province on 8 August 2017. It occurred at the northeastern boundary of the Bayan Har block. The Jiuzhaigou earthquake was one of the largest earthquakes in continental China since the 2013 M s7.0 Lushan earthquake, and it was widely felt across Sichuan and adjacent provinces. The earthquake left 25 dead and up to 500 injured. Because the Jiuzhaigou earthquake did not produce obvious surface ruptures, the causative fault of this event was much debated. The shape of the seismogenic fault, the focal depth of the mainshock and the characteristics of the aftershock sequence were also not very clear. The Sichuan earthquake administration deployed 6 temporary seismic stations around the source region within 4 d of the mainshock. In this study, we collected seismic waveform data and phase arrival data recorded by permanent and temporary stations. We present a systematic investigation about the location of the Jiuzhaigou earthquake sequence with high precision. These results provide new constraints for refining earthquake rupture process, constructing seismogenic models, and evaluating regional earthquake risks. The mainshock of the Jiuzhaigou M s7.0 earthquake was relocated using a 3D velocity model. The procedure takes station elevation, topography and the Earth’s ellipticity into consideration. The location of the mainshock was found to be 103.806°E, 33.201°N, and the focal depth to be 20.4 km. The depth of the initial rupture point of the mainshock was estimated to be below 14 km with S-P arrival time difference recorded at the nearest strong motion station. The locations of early aftershocks were corrected with latter aftershocks recorded using dense temporary seismic stations. A double difference algorithm was used to relocate 1-month aftershock sequence of the Jiuzhaigou earthquake. The locations of 3030 aftershocks were here determined. The average location error was found to be 0.16, 0.15, and 0.18 km in the E-W, N-S, and U-D directions, respectively. The relocation results showed that the aftershocks spread approximately 42 km, trending NWW. The aftershock zone was found to connect the Tazang fault to the north and to the Huya fault to the south. The mainshock is located at the center of the aftershock zone, with similar aftershock length at the both sides. There is a ~5 km sparse aftershock segment to the NW of the mainshock which is consistent with large coseismic slip area. This phenomenon can be explained due to the large amount of stress released during the mainshock rupture. The depth of the aftershock in the northwest end was relatively shallow, and the aftershock zone was about 6 km wide. The depth of aftershock in the southeast section was deeper and the area was narrower, about 4 km. The predominant distribution of the focal depth is 4–20 km. The dip angle of the seismogenic fault is steep, with an average value of about 84°, and changes obviously along the strike direction. The seismogenic fault inclined to the southwest in the shallow part and to the northeast in the deep part. The complex fault shape should be considered when constructing seismogenic model and inverting earthquake rupture process. The depth of the initial rupture point of the mainshock is deeper than the centroid depth and average depth of the aftershock sequence, indicating that the earthquake rupture spreads from deep space to shallow. We find that the aftershocks migrated in the along-strike direction with logarithmic time since the mainshock. The length of the aftershock area expanded from 25 to 42 km in 2 d. The rate of spread was approximately 1.3 km/log(s), consistent with aftershock expansion caused by propagating afterslip. There may be afterslip in the source area of the Jiuzhaigou earthquake.

On the role of adhesion and roughness in stick-slip transition at the contact of two bodies: A numerical study

Abstract This paper proposes a boundary element model for the stick-slip transition at the contact of two bodies of dissimilar materials in presence of adhesion due to van der Waals force. The adhesion is modeled using a Dugdale approximation of adhesive energy. The coupling between the normal pressure and shear stresses is included so that there is no full-stick condition, even in the absence of an external shear stress. Furthermore, the evolution of the slip area over the contact area is different from the well-known Cattaneo-Mindlin solution due to the difference in the mechanical properties of the contacting bodies. It is also shown that the adhesion increases the pre-sliding distance and the static friction. While roughness can only increase the former one. However, the combined effect of roughness and adhesion on the pre-sliding distance is not cumulative as these two parameters are found to be symbiotic.

Systematic deficiency of aftershocks in areas of high coseismic slip for large subduction zone earthquakes.

Fault slip during plate boundary earthquakes releases a portion of the shear stress accumulated due to frictional resistance to relative plate motions. Investigation of 101 large [moment magnitude (Mw) ≥ 7] subduction zone plate boundary mainshocks with consistently determined coseismic slip distributions establishes that 15 to 55% of all master event-relocated aftershocks with Mw ≥ 5.2 are located within the slip regions of the mainshock ruptures and few are located in peak slip regions, allowing for uncertainty in the slip models. For the preferred models, cumulative deficiency of aftershocks within the central three-quarters of the scaled slip regions ranges from 15 to 45%, increasing with the total number of observed aftershocks. The spatial gradients of the mainshock coseismic slip concentrate residual shear stress near the slip zone margins and increase stress outside the slip zone, driving both interplate and intraplate aftershock occurrence near the periphery of the mainshock slip. The shear stress reduction in large-slip regions during the mainshock is generally sufficient to preclude further significant rupture during the aftershock sequence, consistent with large-slip areas relocking and not rupturing again for a substantial time.