Tectonic and Geometric Control on Fault Kinematics of the 2021 Mw7.3 Maduo (China) Earthquake Inferred From Interseismic, Coseismic, and Postseismic InSAR Observations

Seismic and field observations indicate that the Mw7.4 Maduo earthquake ruptured the Jiangcuo fault, which is a secondary fault ∼85 km south of the northern boundary of the Bayan Hor block in western China. The kinematic characteristics of the Jiangcuo fault can shed lights on the seismogenic mechanism of this earthquake. Slip rate is one of the key parameters to describe the kinematic features of a fault, which can also provide quantitative evidences for regional seismic hazard assessments. However, due to lack of effective observations, the slip rate of the Jiangcuo fault has not been studied quantitatively. In this study, we consider the interaction between the Jiangcuo fault and the eastern Kunlun fault, and estimate the slip rates of the two faults using the interseismic GPS observations across the seismogenic region. The inferred results show that the slip rates of the Jiangcuo fault and the Tuosuo Lake segment of the Kunlun fault are 1.2±0.8 and 5.4±0.3 mm a−1, respectively. Combining the slip rate with the average slip inferred from the coseismic slip model, the earthquake recurrence interval of the Jiangcuo fault is estimated to be 1800
 −700
 +3700
 years (1100–5500 years). Based on the results derived from previous studies, as well as calculations in this study, we infer that the slip rate of the Kunlun fault may decrease gradually from the Tuosuo Lake segment to the eastern tip. The Jiangcuo fault and its adjacent parallel secondary faults may have absorbed the relative motion of blocks together with the Kunlun fault.

Slip rate of the seismogenic fault of the 2021 Maduo earthquake in western China inferred from GPS observations

The 21 May 2021 Maduo earthquake was the largest event to occur on a secondary fault in the interior of the active Bayanhar block on the north-central Tibetan plateau in the last twenty years. A detailed kinematic study of the Maduo earthquake helps us to better understand the seismogenic environments of the secondary faults within the block, and its relationship with the block-bounding faults. In this study, firstly, SAR images are used to obtain the coseismic deformation fields. Secondly, we use a strain model-based method and steepest descent method (SDM) to resolve the three-dimensional displacement components and to invert the coseismic slip distribution constrained by coseismic displacement fields, respectively. The three-dimensional displacement fields reveal a dominant left-lateral strike-slip motion, local horizontal displacement variations and widely distributed near-fault subsidence/uplift deformation. We prefer a five-segment fault slip model, with well constrained fault geometry featuring different dip angles and striking, constrained by InSAR observations. The peak coseismic slip is estimated to be ~5 m near longitude 98.9°E at a depth of ~4–7 km. Overall, the distribution of the coseismic slip on the fault is highly correlated to the measured surface displacement offsets along the entire rupture. We observe the moderate shallow slip deficit and limited afterslip deformation following the Maduo earthquake, it may indicate the effects of off-fault deformation during the earthquake and stable interseismic creep on the fault. The occurrence of the Maduo earthquake on a subsidiary fault updates the importance and the traditional estimate of the seismic hazards for the Kunlun fault.

Rupture Kinematics and Coseismic Slip Model of the 2021 Mw 7.3 Maduo (China) Earthquake: Implications for the Seismic Hazard of the Kunlun Fault

On 21 May 2021, an earthquake struck Maduo county in Qinghai Province, China, which is the largest earthquake to hit China since the 2008 Wenchuan earthquake. In this paper, ascending/descending Se...

Complete three-dimensional coseismic displacements related to the 2021 Maduo earthquake in Qinghai Province, China from Sentinel-1 and ALOS-2 SAR images

Based on field investigations, interpretations of high-resolution UAV images, and analyses of available InSAR data, we mapped the fault geometry and surface ruptures of the 2021 Mw 7.4 Maduo earthquake that occurred on a low-activity strike-slip fault within the Tibetan Plateau. The results indicate that (a) the earthquake activated a fault that is ∼161 km long and has complicated structural geometry; (b) the surface rupture occurs over a distance of 148 km, but is separated into three distinct segments by two large gaps (38 and 20 km, respectively); (c) within the surface-rupture segments, the horizontal and vertical displacements are typically 0.2–2.6 m (much lower than the InSAR-based slip maximum of 2–6 m at depth) and ≤0.4 m, respectively. The two large gaps of the Maduo surface rupture represent the two largest surface-rupture discontinuities of strike-slip earthquakes ever documented, and coincide with structurally complicated fault portions and near-surface soft sediments. 

Large Surface‐Rupture Gaps and Low Surface Fault Slip of the 2021 M <sub>w</sub> 7.4 Maduo Earthquake Along a Low‐Activity Strike‐Slip Fault, Tibetan Plateau

The 2021 Qinghai Maduo MS7.4 earthquake was one of the strongest earthquakes that occurred in the Bayan Har block of the Tibetan Plateau during the past 30 years, which spatially filled in the gap of strong earthquake in the eastern section of the northern block boundary. In this study, the aftershock sequence within 8 days after the mainshock was relocated by double difference algorithm. The results show that the total length of the aftershock zone is approximately 170 km; the mainshock epicenter is located in the center of the aftershock zone, indicating a bilateral rupture. The aftershocks are mainly distributed along NWW direction with an overall strike of 285°. The focal depth profiles indicate that the seismogenic fault is nearly vertical and dips to southwest or northeast in different sections, indicating a complex geometry. There is an aftershock gap located to the southeast of the mainshock epicenter with a scale of approximately 20 km. At the eastern end of the aftershock zone, horsetail-like branch faults show the terminal effect of a large strike-slip fault. There is a NW-trending aftershock zone on the north side of the western section, which may be a branch fault triggered by the mainshock. The location of the aftershock sequence is close to the eastern section of the Kunlun Mountain Pass-Jiangcuo (KMPJ) fault. The sequence overlaps well with surface trace of the KMPJ fault. We speculate that the KMPJ fault is the main seismogenic fault of the MS7.4 Maduo earthquake.

Aftershock sequence relocation of the 2021 MS7.4 Maduo Earthquake, Qinghai, China

Deep fault slip characteristics in the Xianshuihe-Anninghe-Daliangshan Fault junction region (eastern Tibet) revealed by repeating micro-earthquakes

High-frequency ( > 1 Hz) ambient noise is usually closely related to anthropogenic activities. During the outbreak and spread of the COVID-19, as various anthropogenic activities are restricted, high-frequency ambient noise level has been observed to be reduced on a worldwide scale. The continuous waveform data at dense broadband seismic stations from ChinArray in eastern North China provides a good opportunity to study the temporal and spatial patterns of the ambient noise level in the region, and to further study the influencing factors, such as the topography and the population density. In this study, we calculated the average power spectral density of ambient noise at each station ±90 days around the Spring Festival in 2019 and in 2020, analyzed the noise level at different stations through normal times, Spring Festivals, epidemic control period, and recovery period, and studied the influencing factors of the noise level. We found that normally high-frequency (1-10 Hz) ambient noise correlates well with the surrounding sedimentary thickness: The noise level is higher when the surrounding sedimentary layer is thicker and vice versa. It correlates moderately with local population density and is time-varying due to anthropogenic activities. During the Spring Festival in 2019 and in 2020, and the epidemic control period after the Spring Festival in 2020, the reduction extent of the noise level correlates moderately with both the sedimentary thickness and population density;the ambient noise level reduces more significantly to the south of 40° N than to the north of it in the study region. Considering that the sedimentary thickness beneath each station is not time-varying, the variation in ambient noise level due to anthropogenic activities is clearly amplified by the sedimentary layer. © 2021 Seismological Society of America. All rights reserved.

Ambient noise level in eastern north china from chinarray and its response to covid-19

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave


 On 5 September 2022, an Mw 6.6 strike-slip earthquake occurred in Luding, Sichuan, China. It illuminates the seismic gap on the southern end of Xianshuihe fault zone, that is Moxi segment, and is the most damaging earthquake in Chinese Mainland since 2014. In this article, we use multiple seismological methods to analyze the basic characteristics of the Luding earthquake, including its source parameters, rupture process, aftershock distribution, and further discuss its implications on preseismic fault behavior and impact on short-term seismic hazard. Using near-field stations, we first revisit the source parameters of the mainshock and obtain a much shallower hypocentral depth (∼9.3 km) than previously reported. Next, we jointly inverse the teleseismic P-wave data and near-field strong-motion data to constrain the mainshock rupture process. The coseismic slip consists of two subevents that spans for ∼20 km and shows an overall unilateral rupture to the south-southeast direction. The earthquake has 90% of the seismic moment released in its first 10 s. Third, we relocate the first 34 days of aftershocks with both manual phase picks and cross correlation, and finally obtain 5269 well-located events. The aftershocks reveal a near-vertical Xianshuihe fault and two sets of unmapped faults off the major Xianshuihe fault: one set of strike-slip faults on the north-northwest of rupture and the other one on the west of mainshock that generates the most intense seismicity with prevalent normal faulting. By examining the aftershock evolution and Coulomb stress change, we find that postseismic processes evolve both on and off the major fault, and the western off-fault system has highly variable fault orientations. Finally, we calculate the Coulomb stress change by the Luding earthquake on surrounding faults. Results show that the north Anninghe fault is significantly loaded by the Luding earthquake (>0.1 MPa), which poses high seismic hazard in the short term.

Long Zhang

Papers

Aftershock sequence relocation of the 2021 MS7.4 Maduo Earthquake, Qinghai, China

Deep fault slip characteristics in the Xianshuihe-Anninghe-Daliangshan Fault junction region (eastern Tibet) revealed by repeating micro-earthquakes

Ambient noise level in eastern north china from chinarray and its response to covid-19

Three-dimensional S-wave velocity structure of the crust and upper mantle for the normal fault system beneath the Yinchuan Basin from joint inversion of receiver function and surface wave

2022 Mw 6.6 Luding, China, Earthquake: A Strong Continental Event Illuminating the Moxi Seismic Gap