Kunlun Earthquake Research Articles

Numerical simulation study on the spontaneous rupture process and its influencing factors of the 2001 MS 8.1 Kunlun earthquake in China

On November 14, 2001, the MS 8.1 Kunlun earthquake occurred in the west of Kunlun Mountain pass in the East Kunlun fault zone of the Qinghai-Tibet Plateau, China. The field investigation and the results of kinematic inversion indicate that it is a strike-slip earthquake with a complex rupture process. The study of the spontaneous rupture process of this earthquake and its influencing factors is of great significance for understanding the occurrence mechanism of continental large earthquakes. First, based on the results of geological survey and kinematic inversion, a three-dimensional non-planar fault model is established. Then, using the curved-grid finite difference method (CG-FDM), the dynamic rupture process of the 2001 MS 8.1 Kunlun earthquake is numerically reproduced by adjusting the parameters for numerical simulation experiments. On this basis, the influence of background stress field, fault geometry and friction coefficient on the surface slip distribution, seismic moment rate function and rupture velocity are discussed respectively. The results show that the important reasons for the super-long rupture scale and super-shear rupture velocity of this earthquake may be the clockwise rotation of the maximum horizontal principal compressive stress along the NNE ∼ NE direction and the low friction coefficient distribution on the whole fault surface. The difference between the dynamic and static friction coefficients along the fault strike may be non-uniform, and it may be larger on the main fault than that on the secondary fault. This will result in a higher level of stress drop on the main fault, leading to the occurrence of super-shear rupture and the slip distribution with the Kusai Lake as the macroseismic epicenter. The large local geometric variation along the strike of the main fault may also have some influence on the distribution of co-seismic slip and the location of the super-shear rupture. In addition, the numerical simulation results in this paper confirm the conclusion that the East Kunlun fault zone has low friction coefficient.

Receiver-function imaging of the lithosphere at the Kunlun-Qaidam boundary, Northeast Tibet

We studied the crustal structure and tectonics in the north Tibetan Plateau from the Songpan-Ganzi terrane to the Qaidam Basin using teleseismic receiver-function imaging, across a major lithospheric boundary, the Kunlun-Qaidam boundary, where previous studies suggest a ~15–20-km change in crustal thickness from thicker crust in the Kunlun Mountains to thinner crust in the Qaidam Basin. We report P receiver functions for 70 stations, largely the International Deep Profiling of Tibet and the Himalaya (INDEPTH), phase IV, experiment. Our most dense station coverage is located along the roughly north-south INDEPTH-IV active-source seismic profile at approximately 95° E longitude. Azimuthal and geographical changes in the receiver functions reveal significant changes in crustal structure and Vp/Vs from across the study area. Receiver functions show strong converters that we interpret as the Moho at ~70 km depth beneath the Qiangtang, Songpan-Ganzi terranes and Kunlun Mountains and at ~50 km depth beneath the central Qaidam Basin. This large change in crustal thickness occurs >50 km north of the North Kunlun strike-slip fault, on which the 2001 M8.1 Kunlun earthquake occurred. Receiver functions for some of the stations north of the thickness change at the Kunlun-Qaidam boundary also show a deeper ~70-km bright converter in addition to the 50-km converter. The two converters appear to overlap by up to ~30 km in some locations along the south Qaidam Basin. We combine previous results with these new results to discuss implications for mechanisms for crustal thickening in the north Tibetan Plateau including crustal flow and crustal injection. At depths imaged here, shallower than ~100 km, we see no evidence of southward subduction of Eurasian lithosphere.

Secondary microseisms of North Atlantic windstorms in Central Eurasia—an understanding of an anomalously big bulge of seismic noise before the 2001 November 14 Mw 7.8 Kunlun earthquake

Secondary microseisms of North Atlantic windstorms in Central Eurasia—an understanding of an anomalously big bulge of seismic noise before the 2001 November 14 Mw 7.8 Kunlun earthquake

Global catalog of earthquake rupture velocities shows anticorrelation between stress drop and rupture velocity

Application of the SCARDEC method provides the apparent source time functions together with seismic moment, depth, and focal mechanism, for most of the recent earthquakes with magnitude larger than 5.6–6. Using this large dataset, we have developed a method to systematically invert for the rupture direction and average rupture velocity Vr, when unilateral rupture propagation dominates. The approach is applied to all the shallow (z < 120km) earthquakes of the catalog over the 1992–2015 time period. After a careful validation process, rupture properties for a catalog of 96 earthquakes are obtained. The subsequent analysis of this catalog provides several insights about the seismic rupture process. We first report that up-dip ruptures are more abundant than down-dip ruptures for shallow subduction interface earthquakes, which can be understood as a consequence of the material contrast between the slab and the overriding crust. Rupture velocities, which are searched without any a-priori up to the maximal P wave velocity (6000–8000m/s), are found between 1200m/s and 4500m/s. This observation indicates that no earthquakes propagate over long distances with rupture velocity approaching the P wave velocity. Among the 23 ruptures faster than 3100m/s, we observe both documented supershear ruptures (e.g. the 2001 Kunlun earthquake), and undocumented ruptures that very likely include a supershear phase. We also find that the correlation of Vr with the source duration scaled to the seismic moment (Ts) is very weak. This directly implies that both Ts and Vr are anticorrelated with the stress drop Δσ. This result has implications for the assessment of the peak ground acceleration (PGA) variability. As shown by Causse and Song (2015), an anticorrelation between Δσ and Vr significantly reduces the predicted PGA variability, and brings it closer to the observed variability.

Activation of a Minor Graben and Pull‐Apart Basin Just East of Bukadaban during the 2001 Kunlun Earthquake (Mw 7.8)

Abstract Surface ruptures found east of the high peak of Bukadaban that formed during the 2001 Kunlun earthquake reveal a minor northeast–southwest‐trending graben, across which oblique approximately east–west extension occurred. Scarps along the southeast flank of the graben indicate vertical components of slip of 3–4 m, and left steps in the trace suggest a component of left‐lateral slip. Scarps on the northwest flank show vertical components of only ∼1.5 m; east–west‐trending ridges in the flanking footwall and hanging wall imply north–south shortening and therefore also a component of left‐lateral slip. These observations corroborate the inference made by others that Bukadaban, though >6000 m high, lies within or adjacent to an active pull‐apart basin between two major strike‐slip segments oriented ∼N100°E.

SLIP MODEL OF THE 2001 KUNLUN MOUNTAIN MS8.1 EARTHQUAKE BY SDM: JOINT INVERSION FROM GPS AND INSAR DATA

AbstractFor the 2001 MS8.1 Kunlun earthquake, which was one of the largest events occurred around the Tibet plateau, a large controversy still exists about its rupture detail. In this paper, we invert the co‐seismic GPS and InSAR data for a robust finite‐fault model of the Kunlun earthquake based on a realistic fault geometry buried in a layered earth structure. The inversion is based on the constrained least‐squares principle and realized using the steepest decent method (SDM). The different data sets are weighted according to their variance and spatial coverage. The results show that the slip maximum can reach up to ∼6.9 m and is located at 35.76° N and 93.40° E. The main rupture area is located at the shallow depth above 20 km. The inverted shallow slip agrees with the surface rupture observed by the field survey, and the whole slip pattern appears generally consistent with the results obtained from previous geological and seismic wave studies.

Estimating high frequency energy radiation of large earthquakes by image deconvolution back-projection

High frequency energy radiation of large earthquakes is a key to evaluating shaking damage and is an important source characteristic for understanding rupture dynamics. We developed a new inversion method, Image Deconvolution Back-Projection (IDBP) to retrieve high frequency energy radiation of seismic sources by linear inversion of observed images from a back-projection approach. The observed back-projection image for multiple sources is considered as a convolution of the image of the true radiated energy and the array response for a point source. The array response that spreads energy both in space and time is evaluated by using data of a smaller reference earthquake that can be assumed to be a point source. The synthetic test of the method shows that the spatial and temporal resolution of the source is much better than that for the conventional back-projection method. We applied this new method to the 2001 Mw 7.8 Kunlun earthquake using data recorded by Hi-net in Japan. The new method resolves a sharp image of the high frequency energy radiation with a significant portion of supershear rupture.

Strike-slip earthquakes can also be detected in the ionosphere

It is generally assumed that co-seismic ionospheric disturbances are generated by large vertical static displacements of the ground during an earthquake. Consequently, it is expected that co-seismic ionospheric disturbances are only observable after earthquakes with a significant dip–slip component. Therefore, earthquakes dominated by strike-slip motion, i.e. with very little vertical co-seismic component, are not expected to generate ionospheric perturbations. In this work, we use total electron content (TEC) measurements from ground-based GNSS-receivers to study ionospheric response to six recent largest strike-slip earthquakes: the Mw7.8 Kunlun earthquake of 14 November 2001, the Mw8.1 Macquarie earthquake of 23 December 2004, the Sumatra earthquake doublet, Mw8.6 and Mw8.2, of 11 April 2012, the Mw7.7 Balochistan earthquake of 24 September 2013 and the Mw 7.7 Scotia Sea earthquake of 17 November 2013. We show that large strike-slip earthquakes generate large ionospheric perturbations of amplitude comparable with those induced by dip–slip earthquakes of equivalent magnitude. We consider that in the absence of significant vertical static co-seismic displacements of the ground, other seismological parameters (primarily the magnitude of co-seismic horizontal displacements, seismic fault dimensions, seismic slip) may contribute in generation of large-amplitude ionospheric perturbations.

Short- and long-term earthquake triggering along the strike-slip Kunlun fault, China: Insights gained from the Ms 8.1 Kunlun earthquake and other modern large earthquakes

Abstract Following the 2001 Ms8.1 Kunlun earthquake, earthquake records of more than 10 years, in addition to more than one century's records of large earthquakes, provide us with a chance to examine short-term (days to a few years) and long-term (years to decades) seismic triggering following a magnitude ~ 8 continental earthquake along a very long strike-slip fault, the Kunlun fault system, located in northern Tibet, China. Based on the calculations of coseismic Coulomb stress changes (ΔCFS) from the larger earthquake and post-seismic stress changes due to viscoelastic stress relaxation in the lower crust and upper mantle, we examined the temporal evolution of seismic triggering. The ETAS (epidemic type aftershocks sequence) model shows that the seismic rate in the aftershock area over ~ 10 years was higher than the background seismicity before the mainshock. Moreover, we discuss long-term (years to decades) triggering and the evolution of stress changes for the sequence of five large earthquakes of M ≥ 7.0 that ruptured the Kunlun fault system since 1937. All subsequent events of M ≥ 7.0 occurred in the regions of positive accumulated ΔCFS. These results show that short-term (up to 200 days in our case) triggering along the strike-slip Kunlun fault is governed by coseismic stress changes, while long-term triggering is somewhat due to post-seismic Coulomb stress changes resulting from viscoelastic relaxation.

Remote triggering of non-volcanic tremor around Taiwan

SUMMARY We perform a systematic survey of triggered deep ‘non-volcanic’ tremor beneath the Central Range (CR) in Taiwan for 45 teleseismic earthquakes from 1998 to 2009 with Mw≥ 7.5 and epicentral distance ≥1000 km to the broad-band station TPUB. Triggered tremors are visually identified as bursts of high-frequency (2–8 Hz), non-impulsive and long-duration seismic energy that are coherent among many seismic stations and modulated by the teleseismic surface waves. Out of the 45 earthquakes, we identified nine teleseismic events associated with nine tremor sources in the southern and five in the northern CR. Most of the tremor sources are located within the depth range of 15–25 km in the lower crust above the Moho. We find that the amplitudes of the surface waves play an important role in determining the triggering potential, and the apparent triggering threshold is ∼0.1 cm s−1, or 7–8 KPa. However, such threshold is partially controlled by the background noise level, which could prevent weaker tremor triggered by surface waves with smaller amplitudes from being identified. The amplitudes of the triggered tremor show a positive correlation with the amplitudes of the triggering surface waves, consistent with the predictions by the ‘clock-advance’ model. In addition to amplitudes, other factors, such as frequency contents and incidence angles, also affect the triggering potential. We find that intermediate-period (30–10 s) surface waves could trigger/modulate tremors, suggesting that long-period (>30 s) surface waves are not always required in long-range triggering. Tremors appear to be triggered by both Love and Rayleigh waves. When the incidence angles are parallel to the strike of the CR, all six events triggered tremor primarily during the Rayleigh waves. For strike normal incidence, only the 2001 Mw7.8 Kunlun earthquake showed predominant Love-wave triggering. This observation can be qualitatively explained by a simple Coulomb failure for a left-lateral shear on the low-angle detachment fault beneath the southern CR.

Riedel shear structures in the co-seismic surface rupture zone produced by the 2001 M w 7.8 Kunlun earthquake, northern Tibetan Plateau

We present a case study of Riedel shear structures related to the co-seismic surface ruptures produced during the 2001 M w 7.8 Kunlun earthquake in northern Tibet, which are related to strike-slip movement along the Kunlun Fault. Field investigations and interpretations of high-resolution remote sensing images show that the 2001 co-seismic surface ruptures, striking WNW–ESE, are mainly characterized by Riedel shear structures, including T fractures, and R, Y, and P shears. A left-lateral shear sense is indicated. To assess the Riedel shear fabrics quantitatively, we measured the azimuth of 19,455 co-seismic surface rupture strands, the width of rupture zones at 474 profiles, and 336 fold axes of mole track structures, using 1-m-resolution IKONOS and 0.61-m-resolution QuickBird images acquired soon after the earthquake. The analytical results show that i) the co-seismic surface ruptures are generally concentrated in up to five subparallel sub-rupture zones, with individual sub-rupture zones varying in width from 3 to 350 m (generally <100 m); ii) the total width across all sub-rupture zones is generally <500 m (though locally >1–2 km); iii) T fractures are mainly developed within the alluvial deposits at counterclockwise angles of 15–40° relative to the general trend of the rupture zone; iv) P shears are also mainly found in the alluvial deposits, but at counterclockwise to clockwise angles of 5–10° relative to the general trend; and v) Y and R shears are developed within both the alluvial deposits and basement rocks, mainly representing the reactivation of pre-existing fault traces. The results demonstrate that the co-seismic Riedel shear structures are primarily controlled by the local geology during surface rupture formation, consistent with the idea that Riedel shear structures are common fault patterns within strike-slip shear zones and that their development is related to the early stages of fault evolution.

Weakness of the Intracontinental Strike-Slip Kunlun Fault and Implications for Tibetan Tectonics

An analysis of fault-related fold structures and the focal mechanisms of large earthquakes reveals that the maximum horizontal stress is oriented sub-perpendicular to the intracontinental strike-slip Kunlun Fault, which triggered the 1997 Mw 7.6 Manyi and 2001 Mw 7.8 Kunlun earthquakes upon the northern Tibetan Plateau. Based on seismic inversion results and in situ measurements of stress performed immediately before and after the 2001 Mw 7.8 Kunlun earthquake, a low shear stress of <1 MPa is estimated for the Kunlun Fault, which is an order of magnitude less than the shear strength obtained from laboratory measurements but compatible with that measured along the San Andreas Fault. Geological and geophysical evidence confirms that the Kunlun Fault is rheologically weak and that it plays an important role in accommodating eastward extrusion of the Tibetan Plateau in response to ongoing continental collision between the Indian and Eurasian plates.

Short‐time postseismic deformation of 2001 Ms8.1 Kunlun (China) earthquake

AbstractAfter the Ms 8.1 Kunlun earthquake, postseismic displacements were resolved with GPS. The observed data showed that there were significant differences between the deformations on the south and the north sides of the Kunlun fault. In addition, it is shown that the direction of deformation on the north side shifted from westward to eastward after a short‐time adjustment. Such GPS data are used as the constraints in finite element method (FEM) modeling of postseismic deformation. Using 3D poro‐viscoelastic model, we show that the horizontal inhomogeneous viscosities in lower crust can play an important role in the geodynamic behavior. The best‐fitting viscosities of lower crust are about 5.0×1017 Pa s, 9.0×1018 Pa s in Qiangtang block and Qaidam basin, respectively. The simulation suggests that the postseismic deformation of 2001 Kunlun Ms8.1 earthquake probably be caused by both the viscoelastic relaxation and poroelastic rebound. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Mechanisms of Transient Postseismic Deformation Following the 2001 Mw 7.8 Kunlun (China) Earthquake

Using global positioning system (GPS) technology, significant postseismic surface displacements were observed within the first 4 months after the 2001 Mw 7.8 Kunlun earthquake which occurred in China. In this study, we investigated the mechanisms that may have possibly contributed to the postseismic deformations that have been observed. Based on the modeling results, we find that an afterslip model can interpret postseismic displacements in the near field even when the fault plane is extended to the bottom of the crust (~70 km). Models based on the viscoelastic relaxation theory showed a large discrepancy in the spatial pattern of the deformation compared with what has been observed. Thus, we infer that both mechanisms cannot interpret the observed postseismic deformation independently. A combination of afterslip and viscoelastic relaxation can further improve the data fit, especially at sites far from the fault. With maximum afterslip of ~0.4 m occurring at a depth of 10 km in the central section, the combined model shows that the estimated afterslip occurred mostly on and below the coseismic rupture plane, as well as on its eastern extension. The estimated moment released by the afterslip in the first 4 months is almost 40% of that released by the coseismic slip. The best-fitting viscoelastic relaxation model shows a “weak” upper mantle with a viscosity of ~1.0 × 1018 Pa s. The combined model also suggests the existence of a lower crust with viscosity larger than 1.0 × 1018 Pa s, although it cannot be constrained accurately.

Erratum to: Estimation of the 2001 Kunlun earthquake fault slip from GPS coseismic data using Hori’s inverse method

The Hori’s inverse method based on spectral decomposition was applied to estimate coseismic slip distribution on the rupture plane of the 14 November 2001 MS8.1 Kunlun earthquake based on GPS survey results. The inversion result shows that the six sliding models can be constrained by the coseismic GPS data. The established slips mainly concentrated along the eastern segment of the fault rupture, and the maximum magnitude is about 7 m. Slip on the eastern segment of the fault rupture represents as purely left-lateral strike-slip. Slip on the western segment of the seismic rupture represents as mainly dip-slip with the maximum dip-slip about 1 m. Total predicted scalar seismic moment is 5.196×1020 N·m. Our results constrained by geodetic data are consistent with seismological results.

Estimation of the 2001 Kunlun earthquake fault slip from GPS coseismic data using Hori’s inverse method

The Hori’s inverse method based on spectral decomposition was applied to estimate coseismic slip distribution on the rupture plane of the 14 November 2001 MS8.1 Kunlun earthquake based on GPS survey results. The inversion result shows that the six sliding models can be constrained by the coseismic GPS data. The established slips mainly concentrated along the eastern segment of the fault rupture, and the maximum magnitude is about 7 m. Slip on the eastern segment of the fault rupture represents as purely left-lateral strike-slip. Slip on the western segment of the seismic rupture represents as mainly dip-slip with the maximum dip-slip about 1 m. Total predicted scalar seismic moment is 5.196×1020 N·m. Our results constrained by geodetic data are consistent with seismological results.

Fault zone structures of northern and southern portions of the main central fault generated by the 2008 Wenchuan earthquake using fault zone trapped waves

The rupture process of the May 12, 2008 MS8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170–200 m and 200–230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of M8.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.

Shallow seismic structure of Kunlun fault zone in northern Tibetan Plateau, China: implications for the 2001Ms8.1 Kunlun earthquake

SUMMARY The shallow seismic velocity structure of the Kunlun fault zone (KLFZ) was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions. The data were collected after the 2001 Kunlun Ms8.1 earthquake in the northern Tibetan Plateau. Seismic phases for the in-line record sections (26 records up to a distance of 15 km) along the fault zone were analysed, and 1-D P- and S-wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method. Sixteen seismic stations were deployed along the off-line profile perpendicular to the fault zone. Fault-zone trapped waves appear clearly on the record sections, which were simulated with a 3-D finite difference algorithm. Quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the Kunlun fault-zone width is 300 m, and S-wave quality factor Q within the fault zone is 15. Significantly, S-wave velocities within the fault zone are reduced by 30–45 per cent from surrounding rocks to a depth of at least 1–2 km, while P-wave velocities are reduced by 7–20 per cent. A fault-zone with such Pand S-low velocities is an indication of high fluid pressure because Vs is affected more than Vp. The low-velocity and low-Q zone in the KLFZ model is the effect of multiple ruptures along the fault trace of the 2001 Ms8.1 Kunlun earthquake.

Studying the viscosity of lower crust of Qinghai-Tibet Plateau according to post-seismic deformation

The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in quantitative research on geodynamics. Its order of magnitude will have a great influence on the results of quantitative modeling. To obtain the viscosity of lower crust of Qinghai-Tibet Plateau, this parameter was calculated by three methods. The first is based on the estimation on the temperature state of Qinghai-Tibet Plateau in the deep part, and the viscosity of lower crust of northern Plateau was recomputed with strain rate derived from rheology law and GPS observation. Effective viscosity of middle crust in Kunlun region is between 1020 and 1022 Pa·s, and that of lower crust is between 1019 and 1021 Pa·s; the second is based on three kinds of rheological models used to fit the post-seismic deformation recorded by cross-over fault GPS sites set after M s8.1 Kunlun earthquake in 2001. The viscosity of lower crust obtained by this method is of 1017 Pa·s order of magnitude. However, higher viscosity is required to fit the data of south fault better, and the lower one is required to fit the data of north fault better. The viscosity of lower crust, which was obtained by fitting the cross-over fault post-seismic deformation after M s7.6 Luhuo earthquake in 1973, is of 1019 Pa·s order of magnitude. Non-linear relationship between effective viscosity and strain rate is ignored in the former research of effective viscosity. This research shows the difference of effective viscosity obtained from laboratory experiment, and shorter and longer time post-seismic deformation after large earthquakes can be explained in phase.

Prehistoric seismicity-induced liquefaction along the western segment of the strike-slip Kunlun fault, northern Tibet

Abstract The 2001 M w 7.8 Kunlun earthquake occurred in northern Tibet, and produced a 450-km-long surface rupture zone along the western segment of the strike-slip Kunlun fault. There are, however, no historic or instrumental records of large earthquakes in this fault segment. Field investigations of liquefaction structures and radiocarbon dating results reveal that at least three large earthquakes, including the 2001 earthquake, occurred in the western segment of the Kunlun fault during the past seven to nine centuries. Liquefaction structures formed in alluvial deposits composed of sand-gravel yielding 14 C ages of 679–901 yr bp are observed on the current stream channel which is sinistrally offset 75–82 m, including 3–6 m displacement produced by the 2001 event. On the basis of the field investigations and 14 C dating results, we conclude that the liquefaction structures and subsequent faulting events were caused by at least two large earthquakes of M&gt;7 prior to the 2001 earthquake and the average recurrence interval of large earthquakes is estimated to be about 400 years in the late Holocene.