Complex Slip Distribution of the 2021 Mw 7.4 Maduo, China, Earthquake: An Event Occurring on the Slowly Slipping Fault

Abstract The 21 May 2021 Maduo earthquake occurred on the Kunlun Mountain Pass–Jiangcuo fault (KMPJF), a seismogenic fault with no documented large earthquakes. To probe its kinematics, we first estimate the slip rates of the KMPJF and Tuosuo Lake segment (TLS, ∼75 km north of the KMPJF) of the East Kunlun fault (EKLF) based on the secular Global Positioning System (GPS) data using the Markov chain Monte Carlo method. Our model reveals that the slip rates of the KMPJF and TLS are 1.7 ± 0.8 and 7.1 ± 0.3 mm/yr, respectively. Then, we invert high-resolution GPS and Interferometric Synthetic Aperture Radar observations to decipher the fault geometry and detailed coseismic slip distribution associated with the Maduo earthquake. The geometry of the KMPFJ significantly varies along strike, composed of five fault subsegments. The most slip is accommodated by two steeply dipping fault segments, with the patch of large sinistral slip concentrated in the shallow depth on a simple straight structure. The released seismic moment is ∼1.5×1020 N·m, equivalent to an Mw 7.39 event, with a peak slip of ∼9.3 m. Combining the average coseismic slip and slip rate of the main fault, an earthquake recurrence period of ∼1250−400+1120 yr is estimated. The Maduo earthquake reminds us to reevaluate the potential of seismic gaps where slip rates are low. Based on our calculated Coulomb failure stress, the Maduo earthquake imposes positive stress on the Maqin–Maqu segment of the EKLF, a long-recognized seismic gap, implying that it may accelerate the occurrence of the next major event in this region.

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A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California

Science Advances ◽

10.1126/sciadv.aaz5691 ◽

2021 ◽

Vol 7 (13) ◽

pp. eaaz5691

Author(s):

Kimberly Blisniuk ◽

Katherine Scharer ◽

Warren D. Sharp ◽

Roland Burgmann ◽

Colin Amos ◽

...

Keyword(s):

Los Angeles ◽

Southern California ◽

San Andreas Fault ◽

Slip Rate ◽

Large Magnitude ◽

Slip Rates ◽

San Andreas ◽

The Pacific ◽

Large Earthquakes ◽

Dependent Probability

The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand.

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Tectonic Geomorphology and Paleoseismology of the Sharkhai fault: a new source of seismic hazard for Ulaanbaatar (Mongolia)

10.5194/se-2021-91 ◽

2021 ◽

Author(s):

Abeer Al-Ashkar ◽

Antoine Schlupp ◽

Matthieu Ferry ◽

Ulziibat Munkhuu

Keyword(s):

Seismic Hazard ◽

Scaling Laws ◽

Active Faults ◽

Seismic Hazard Assessment ◽

Capital City ◽

Tectonic Geomorphology ◽

Time Interval ◽

Coseismic Slip ◽

Slip Rates ◽

Large Earthquakes

Abstract. We present new constraints from tectonic geomorphology and paleoseismology along the newly discovered Sharkhai fault near the capital city of Mongolia. Detailed observations from high resolution Pleiades satellite images and field investigations allowed us to map the fault in detail, describe its geometry and segmentation, characterize its kinematics, and document its recent activity and seismic behavior (cumulative displacements and paleoseismicity). The Sharkhai fault displays a surface length of ~40 km with a slightly arcuate geometry, and a strike ranging from N42° E to N72° E. It affects numerous drainages that show left-lateral cumulative displacements reaching 57 m. Paleoseismic investigations document the faulting and deposition record for the last ~3000 yr and reveal that the penultimate earthquake (PE) occurred between 1515 ± 90 BC and 945 ± 110 BC and the most recent event (MRE) occurred after 860 ± 85 AD. The resulting time interval of 2080 ± 470 years is the first constraint on the Sharkhai fault for large earthquakes. On the basis of our mapping of the surface rupture and the resulting segmentation analysis, we propose two possible scenarios for large earthquakes with likely magnitudes between 6.4 ± 0.2 and 7.1 ± 0.2. Furthermore, we apply scaling laws to infer coseismic slip values and derive preliminary estimates of long-term slip rates between 0.2 ± 0.2 and 1.0 ± 0.5 mm/y. Finally, we propose that these original observations and results from a newly discovered fault should be taken into account for the seismic hazard assessment for the city of Ulaanbaatar and help build a comprehensive model of active faults in that region.

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Paleoearthquakes on the Húsavík-Flatey Fault in northern Iceland: Where are the large earthquakes?

10.5194/egusphere-egu21-13998 ◽

2021 ◽

Author(s):

Remi Matrau ◽

Yann Klinger ◽

Jonathan Harrington ◽

Ulas Avsar ◽

Esther R. Gudmundsdottir ◽

...

Keyword(s):

Slip Rate ◽

Late Glacial ◽

Fault Scarp ◽

Alluvial Fan ◽

Tectonic Deformation ◽

Birch Wood ◽

Alluvial Deposits ◽

Slip Rates ◽

Tephra Layers ◽

Large Earthquakes

Paleoseismology is key to study earthquake recurrence and fault slip rates during the Late Pleistocene-Holocene. The H&#250;sav&#237;k-Flatey Fault (HFF) in northern Iceland is a 100 km-long right-lateral transform fault connecting the onshore Northern Volcanic Zone to the offshore Kolbeinsey Ridge and accommodating, together with the Gr&#237;msey Oblique Rift (GOR), ~18 mm/yr of relative motion between the Eurasian and North American plates. Significant earthquakes occurred on the HFF in 1755, 1838 and 1872 with estimated magnitudes of 6.5-7. However, historical information on past earthquakes prior to 1755 is very limited in both timing and size.We excavated five trenches in a small basin (Vestari Krubbssk&#225;l) located 5.5 km southeast of the town of H&#250;sav&#237;k and at 300 m.a.s.l. and one trench in an alluvial fan (Tra&#240;arger&#240;i) located 0.5 km north of H&#250;sav&#237;k and at 50 m.a.s.l. In a cold and wet environment, such as in coastal parts of Iceland, one has to take into account periglacial processes affecting the topsoil to discriminate tectonic from non-tectonic deformation. We used tephra layers in the Vestari Krubbssk&#225;l and Tra&#240;arger&#240;i trenches as well as birch wood samples in Tra&#240;arger&#240;i to constrain the timing of past earthquakes. Tephra layers Hekla-3 (2971 BP) and Hekla-4 (4331&#177;20 BP) are visible in the top half of all the trenches. In addition, a few younger tephra layers are visible in the top part of the trenches. In Tra&#240;arger&#240;i several dark layers rich in organic matter are found, including birch wood-rich layers from the Earlier Birch Period (9000-7000 BP) and the Later Birch Period (5000-2500 BP). In Vestari Krubbssk&#225;l the lower halves of the trenches display mostly lacustrine deposits whereas in Tra&#240;arger&#240;i the lower half of the trench shows alluvial deposits overlaying coarser deposits (gravels/pebbles) most likely of late-glacial or early post-glacial origins. In addition, early Holocene tephra layers are observed in some of the trenches at both sites and may correspond to Askja-S (10800 BP), Saksunarvatn (10300 BP) and Vedde (12100 BP). These observations provide good age constraints and suggest that both the Vestari Krubbssk&#225;l and Tra&#240;arger&#240;i trenches cover the entire Holocene.Trenches at both sites show significant normal deformation in addition to strike-slip, well correlated with their larger scale topographies (pull-apart basin in Vestari Krubbssk&#225;l and 45 m-high fault scarp in Tra&#240;arger&#240;i). We mapped layers, cracks and faults on all trench walls to build a catalogue of Holocene earthquakes. We identified events based on the upward terminations of the cracks and retrodeformation. Our results yield fewer major earthquakes than expected, suggesting that large earthquakes (around magnitude 7) are probably rare and the more typical HFF earthquakes of magnitude 6-6.5 likely produce limited topsoil deformation.[yk1]&#160; Our interpretation also suggests that the Holocene slip rate [yk2]&#160;for the fault section we are studying may be slower than the estimated geodetic slip rate (6 to 9 mm/yr)[yk3]&#160; for the entire onshore HFF, although secondary onshore sub-parallel fault strands could accommodate part of the deformation.

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Multisegment Rupture Hazard Modeling along the Xianshuihe Fault Zone, Southeastern Tibetan Plateau

Seismological Research Letters ◽

10.1785/0220200117 ◽

2020 ◽

Author(s):

Jia Cheng ◽

Thomas Chartier ◽

Xiwei Xu

Keyword(s):

Slip Rate ◽

Historical Earthquakes ◽

Input Constraints ◽

Ground Acceleration ◽

Slip Rates ◽

Fault Slip Rates ◽

Seismicity Rates ◽

Xianshuihe Fault Zone ◽

Large Earthquakes ◽

Southern Section

Abstract The Xianshuihe fault is a remarkable strike-slip fault characterized by high slip rate (∼10 mm/yr) and frequent strong historical earthquakes. The potential for future large earthquakes on this fault is enhanced by the 2008 Mw 7.9 Wenchuan earthquake. Previous works gave little attention to the probabilities of multisegment ruptures on the Xianshuihe fault. In this study, we build five possible multisegment rupture combination models for the Xianshuihe fault. The fault slip rates and historical earthquakes are used as input constraints to model the future seismicity on the fault segments and test whether the rupture combination models are appropriate. The segment combination model, based essentially on historical ruptures, has produced the seismicity rates most consistent with the historical records, although the model with ruptures on both the entire northern section and southern section should also be considered. The peak ground acceleration values with a return period of 475 yr calculated using the modeled rates on the Xianshuihe fault for both two models are on average larger than the values of the China Seismic Ground Motion Parameters Zonation Map.

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The impact of earthquake cycle variability on neotectonic and paleoseismic slip rate estimates

Solid Earth ◽

10.5194/se-10-15-2019 ◽

2019 ◽

Vol 10 (1) ◽

pp. 15-25 ◽

Cited By ~ 7

Author(s):

Richard Styron

Keyword(s):

Late Quaternary ◽

Epistemic Uncertainty ◽

Slip Rate ◽

Earthquake Recurrence ◽

Coseismic Slip ◽

Slip Rates ◽

True Value ◽

Recurrence Intervals ◽

The Impact ◽

Earthquake Cycles

Abstract. Because of the natural (aleatoric) variability in earthquake recurrence intervals and coseismic displacements on a fault, cumulative slip on a fault does not increase linearly or perfectly step-wise with time; instead, some amount of variability in shorter-term slip rates results. Though this variability could greatly affect the accuracy of neotectonic (i.e., late Quaternary) and paleoseismic slip rate estimates, these effects have not been quantified. In this study, idealized faults with four different, representative, earthquake recurrence distributions are created with equal mean recurrence intervals (1000 years) and coseismic slip distributions, and the variability in slip rate estimates over 500- to 100 000-year measurement windows is calculated for all faults through Monte Carlo simulations. Slip rates are calculated as net offset divided by elapsed time, as in a typical neotectonic study. The recurrence distributions used are quasi-periodic, unclustered and clustered lognormal distributions, and an unclustered exponential distribution. The results demonstrate that the most important parameter is the coefficient of variation (CV = standard deviation ∕ mean) of the recurrence distributions rather than the shape of the distribution itself. Slip rate variability over short timescales (< 5000 years or 5 mean earthquake cycles) is quite high, varying by a factor of 3 or more from the mean, but decreases with time and is close to stable after ∼40 000 years (40 mean earthquake cycles). This variability is higher for recurrence distributions with a higher CV. The natural variability in the slip rate estimates compared to the true value is then used to estimate the epistemic uncertainty in a single slip rate measurement (as one would make in a geological study) in the absence of any measurement uncertainty. This epistemic uncertainty is very high (a factor of 2 or more) for measurement windows of a few mean earthquake cycles (as in a paleoseismic slip rate estimate), but decreases rapidly to a factor of 1–2 with > 5 mean earthquake cycles (as in a neotectonic slip rate study). These uncertainties are independent of, and should be propagated with, uncertainties in fault displacement and geochronologic measurements used to estimate slip rates. They may then aid in the comparison of slip rates from different methods or the evaluation of potential slip rate changes over time.

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Stochastic time-predictable model for earthquake occurrences

Bulletin of the Seismological Society of America ◽

10.1785/bssa0740062593 ◽

1984 ◽

Vol 74 (6) ◽

pp. 2593-2611

Author(s):

T. Anagnos ◽

A. S. Kiremidjian

Keyword(s):

Seismic Hazard ◽

Slip Rate ◽

Poisson Model ◽

Sensitivity Analyses ◽

Seismic Gap ◽

Temporal Dependence ◽

Slip Rates ◽

Poisson Models ◽

Recurrence Model ◽

Stochastic Time

Abstract Recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated. This observation is the basis for the deterministic time-predictable recurrence model of Shimazaki and Nakata. Using the basic assumptions of the time-predictable recurrence model, we develop a stochastic model of earthquake occurrence that incorporates temporal dependence. This paper discusses the formulation of the model and the effect of including temporal dependence. Hazard estimates for a section of the San Andreas fault near Parkfield, where data has suggested time-predictable behavior, are obtained for illustrative purposes. Comparisons are made with the Poisson model. Results indicate that currently used Poisson models may give lower estimates of the seismic hazard when there has been a seismic gap. Of the various sensitivity analyses performed, it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time-predictable model. Therefore, accurate determinations of slip rates (both seismic and aseismic) can substantially reduce the uncertainty in seismic hazard estimates.

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Present Seismotectonic Behavior of the EAF from Improved Seismicity Catalog and Earthquake Source Mechanism Solutions

10.5194/egusphere-egu2020-18053 ◽

2020 ◽

Author(s):

Sezim Ezgi Guvercin ◽

Hayrullah Karabulut ◽

Ugur Dogan ◽

Ziyadin Cakir ◽

Semih Ergintav ◽

...

Keyword(s):

Surface Deformation ◽

Complex Structure ◽

Slip Rate ◽

Earthquake Source ◽

Slip Rates ◽

North East ◽

The North ◽

Source Mechanisms ◽

Seismicity Catalog ◽

Large Earthquakes

The seismotectonic behavior of the Eastern Anatolia is predominantly controlled by the East Anatolian Fault (EAF). Together with the North Anatolian Fault (NAF), this ~400 km long sinistral transform fault, accommodates the westward motion of Anatolia between Anatolian and Arabian plates with a slip rate of ~10 mm/yr which is significantly slower than the motion of the NAF (25 mm/yr). Although this two major faults are similar in terms of the migration of the large earthquakes from east to west, the present seismicity of the EAF is high compared to the NAF. Except for the several earthquakes with Mw > 5, there were no devastating earthquakes during the instrumental period along the EAF. The absence of large earthquakes during the last ~50 years along the EAF indicates presence of significant seismic gaps and potential seismic hazard in the region. Recent studies indicate segmentation of the EAF with varying lengths of creeping and locked segments. Some details of the geometries and the slip rates of these segments have been estimated by the InSAR observations. Both InSAR and GPS observations indicate that the maximum creep along this the EAF is ~10 mm/yr, approximately the slip rate of the EAF.While both geodetic data verify the existence of creep from surface deformation, its relation to the seismic behavior of the EAF is less clear. There is a ~30 km long creeping segment to the north-east of Lake Hazar which generates no significant seismicity. On the other hand, another creeping segment to the south-west of Lake Hazar, there are repeating events, below the depth of 10 km, with a horizontal extent of 15 km. The highly fractured and complex structure of this fault zone is also confirmed by the available focal mechanisms which shows significant variety.In this study, we update seismicity catalog with improved locations to date and present a uniform and high quality focal mechanism catalog down to M4 completeness, using regional waveforms. The seismicity catalog is used to estimate the geometry of the segmentation while the novel earthquake source mechanisms are used to understand the kinematics of the segments and interactions. Moreover, we present the latest M4.9, 2019, Sivrice earthquake, pointing out a location where the stress is perturbed due to a transition from creeping segment to locked segment. (Supported by TUBITAK no: 118Y435 project)

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Surface Rupture Kinematics and Coseismic Slip Distribution during the 2019 Mw7.1 Ridgecrest, California Earthquake Sequence Revealed by SAR and Optical Images

Remote Sensing ◽

10.3390/rs12233883 ◽

2020 ◽

Vol 12 (23) ◽

pp. 3883

Author(s):

Chenglong Li ◽

Guohong Zhang ◽

Xinjian Shan ◽

Dezheng Zhao ◽

Yanchuan Li ◽

...

Keyword(s):

Strike Slip ◽

Earthquake Sequence ◽

Slip Distribution ◽

Fault System ◽

Seismogenic Fault ◽

Coseismic Slip ◽

Surface Rupture ◽

Lateral Strike Slip ◽

Optical Images ◽

Rupture Kinematics

The 2019 Ridgecrest, California earthquake sequence ruptured along a complex fault system and triggered seismic and aseismic slips on intersecting faults. To characterize the surface rupture kinematics and fault slip distribution, we used optical images and Interferometric Synthetic Aperture Radar (InSAR) observations to reconstruct the displacement caused by the earthquake sequence. We further calculated curl and divergence from the north-south and east-west components, to effectively identify the surface rupture traces. The results show that the major seismogenic fault had a length of ~55 km and strike of 320° and consisted of five secondary faults. On the basis of the determined multiple-fault geometries, we inverted the coseismic slip distributions by InSAR measurements, which indicates that the Mw7.1 mainshock was dominated by the right-lateral strike-slip (maximum strike-slip of ~5.8 m at the depth of ~7.5 km), with a small dip-slip component (peaking at ~1.8 m) on an east-dipping fault. The Mw6.4 foreshock was dominated by the left-lateral strike-slip on a north-dipping fault. These earthquakes triggered obvious aseismic creep along the Garlock fault (117.3° W–117.5° W). These results are consistent with the rupture process of the earthquake sequence, which featured a complicated cascading rupture rather than a single continuous rupture front propagating along multiple faults.

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The impact of earthquake cycle variability on neotectonic and paleoseismic slip rate estimates

10.5194/se-2018-40 ◽

2018 ◽

Cited By ~ 2

Author(s):

Richard Styron

Keyword(s):

Late Quaternary ◽

Slip Rate ◽

Earthquake Recurrence ◽

Coseismic Slip ◽

Slip Rates ◽

Rate Study ◽

Recurrence Intervals ◽

Short Time ◽

Fault Displacement ◽

The Impact

Abstract. Because of the natural variability (aleatoric uncertainty) in earthquake recurrence intervals and coseismic displacements on a fault, cumulative slip on a fault does not increase linearly or perfectly step-wise with time; instead, some amount of variability in shorter-term slip rates results. Though this variability could greatly affect the accuracy of neotectonic (i.e., late Quaternary) and paleoseismic slip rate estimates, these effects have not been quantified. In this study, idealized faults with four different, representative earthquake recurrence distributions are created with equal mean recurrence intervals (1,000 years) and coseismic slip distributions, and the variability in slip rate measurements over 500 to 100,000 year measurement windows is calculated for all faults through Monte Carlo simulations. The recurrence distributions used are quasi-periodic, unclustered and clustered lognormal distributions, and an unclustered exponential distribution. The results demonstrate that the most important parameter is the coefficient of variation (COV = standard deviation/mean) of the recurrence distributions rather than the shape of the distribution itself. Slip rate variability over short time scales ( 5 mean earthquake cycles (as in a neotectonic slip rate study). These uncertainties are independent of, and should be propagated with uncertainties in fault displacement and geochronologic measurements used to estimate slip rates. They may then aid in the comparison of slip rates from different methods or the evaluation of potential slip rate changes over time.

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Which Fault Threatens Me Most? Bridging the Gap Between Geologic Data-Providers and Seismic Risk Practitioners

Frontiers in Earth Science ◽

10.3389/feart.2020.626401 ◽

2021 ◽

Vol 8 ◽

Author(s):

Oona Scotti ◽

Francesco Visini ◽

Joanna Faure Walker ◽

Laura Peruzza ◽

Bruno Pace ◽

...

Keyword(s):

Seismic Hazard ◽

Slip Rate ◽

End Users ◽

Central Apennines ◽

Slip Rates ◽

Relative Contribution ◽

Fault Parameters ◽

Main Fault ◽

Hazard And Risk ◽

Geologic Data

The aim of the Fault2SHA European Seismological Commission Working Group Central Apennines laboratory is to enhance the use of geological data in fault-based seismic hazard and risk assessment and to promote synergies between data providers (earthquake geologists), end-users and decision-makers. Here we use the Fault2SHA Central Apennines Database where geologic data are provided in the form of characterized fault traces, grouped into faults and main faults, with individual slip rate estimates. The proposed methodology first derives slip rate profiles for each main fault. Main faults are then divided into distinct sections of length comparable to the seismogenic depth to allow consideration of variable slip rates and the exploration of multi-fault ruptures in the computations. The methodology further allows exploration of epistemic uncertainties documented in the database (e.g., main fault definition, slip rates) as well as additional parameters required to characterize the seismogenic potential of fault sources (e.g., 3D fault geometries). To illustrate the power of the methodology, in this paper we consider only one branch of the uncertainties affecting each step of the computation procedure. The resulting hazard and typological risk maps allow both data providers and end-users 1) to visualize the faults that threaten specific localities the most, 2) to appreciate the density of observations used for the computation of slip rate profiles, and 3) interrogate the degree of confidence on the fault parameters documented in the database (activity and location certainty). Finally, closing the loop, the methodology highlights priorities for future geological investigations in terms of where improvements in the density of data within the database would lead to the greatest decreases in epistemic uncertainties in the hazard and risk calculations. Key to this new generation of fault-based seismic hazard and risk methodology are the user-friendly open source codes provided with this publication, documenting, step-by-step, the link between the geological database and the relative contribution of each section to seismic hazard and risk at specific localities.

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