DOCSLIB.ORG

Stochastic Characterization and Decision Bases Under Time-Dependent Aftershock Risk in Performance-Based Earthquake Engineering

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Stochastic Characterization and Decision Bases Under Time-Dependent Aftershock Risk in Performance-Based Earthquake Engineering Department of Civil and Environmental Engineering Stanford University STOCHASTIC CHARACTERIZATION AND DECISION BASES UNDER TIME-DEPENDENT AFTERSHOCK RISK IN PERFORMANCE-BASED EARTHQUAKE ENGINEERING by Gee Liek Yeo and C. Allin Cornell Report No. 149 April 2005 The John A. Blume Earthquake Engineering Center was established to promote research and education in earthquake engineering. Through its activities our understanding of earthquakes and their effects on mankind’s facilities and structures is improving. The Center conducts research, provides instruction, publishes reports and articles, conducts seminar and conferences, and provides financial support for students. The Center is named for Dr. John A. Blume, a well-known consulting engineer and Stanford alumnus. Address: The John A. Blume Earthquake Engineering Center Department of Civil and Environmental Engineering Stanford University Stanford CA 94305-4020 (650) 723-4150 (650) 725-9755 (fax) [email protected] http://blume.stanford.edu ©2005 The John A. Blume Earthquake Engineering Center STOCHASTIC CHARACTERIZATION AND DECISION BASES UNDER TIME-DEPENDENT AFTERSHOCK RISK IN PERFORMANCE-BASED EARTHQUAKE ENGINEERING Gee Liek Yeo April 2005 °c Copyright by Gee Liek Yeo 2005 All Rights Reserved ii Preface This thesis addresses the broad role of aftershocks in the Performance-based Earthquake Engineering (PBEE) process. This is an area which has, to date, not received careful scrutiny nor explicit quantitative analysis. I begin by introducing Aftershock Probabilistic Seismic Hazard Analysis (APSHA). APSHA, similar to conventional mainshock PSHA, is a procedure to characterize the time- varying aftershock ground motion hazard at a site. I next show a methodology to quantify, in probabilistic terms, the multi-damage-state capacity of buildings in di®erent post-mainshock damage states. A time-dependent building \tagging" policy (permitting or restricting occu- pancy) is then developed based on the quanti¯cation of life-safety threat in the aftershock environment using the probability of collapse as a proxy for fatality risk. I also develop formal stochastic ¯nancial life-cycle cost models in both the post- and pre-mainshock environment. I include both transition and disruption costs in our model. Transition costs can be attributed to one-time ¯nancial losses due to structural and non- structural damage to the building, and can also include the costs of evacuation of the occupants of a building. Disruption costs can be attributed to the downtime and limited functionality of the damaged building. I begin with the traditional Poisson model for tem- porally homogeneous mainshocks and extend it to nonhomogeneous aftershocks. Further, the model is generalized to include renewal processes for modeling mainshock occurrences and Markov-chain descriptions of the damage states of a building. The analysis procedures are non-homogeneous Markov and semi-Markov decision analysis and stochastic dynamic programming (Howard (1971)). Finally, I introduce a decision analytic framework under improving states of information for both the post- and pre-mainshock environment. I emphasize the role of information in potentially improving our decision-making capability. Decision bases include the expected life-cycle cost and rate of collapse in the aftershock environment. I also introduce the iii concept of the value of information to determine if obtaining more information is ¯nancially desirable, which can potentially improve the quality of the decision. iv Contents Preface iii 1 Introduction 1 1.1 PBEE/PEER . 3 1.2 Signi¯cance of Aftershocks in PBEE . 6 1.3 Challenges of Aftershock Risk Analysis . 8 1.4 Thesis Organization . 15 2 Aftershock Probabilistic Seismic Hazard Analysis 16 2.1 Introduction . 16 2.2 Methodology . 18 2.3 Example . 23 2.3.1 Comparison of Mainshock Hazard to Aftershock Hazard . 24 2.3.2 E®ects of Duration (T ) on Aftershock Hazard . 26 2.3.3 E®ects of Elapsed Time from Initial Rupture (t) on Aftershock Hazard 29 2.3.4 Similarity of APSHA to Mainshock PSHA . 31 2.3.5 E®ects of Mainshock Magnitude (mm) and Site Location on After- shock Hazard . 33 2.3.6 E®ects of Structural Periods (T0) on Aftershock Hazard . 35 2.3.7 Summary and Approximate APSHA . 39 2.4 Correlation between "m and "a ......................... 40 2.5 Conclusion . 44 3 Performance of Mainshock-Damaged Buildings 46 3.1 Methodology . 47 v 3.1.1 Quanti¯cation of aftershock capacity of mainshock-damaged buildings 47 3.1.2 Determination of Transition Probabilities . 49 3.2 Example . 53 3.3 Conclusion . 60 4 Life-safety Based Building Tagging Criteria 62 4.1 Introduction . 63 4.2 Equivalent Constant Rates . 64 4.3 Proposed Building Tagging Methodology . 68 4.4 Tolerable Collapse Rate . 70 4.5 Primary Building Tagging Basis . 71 4.6 Special Tagging Cases: Emergency Workers . 72 4.7 Tagging Basis with Repair . 74 4.8 Simpli¯ed Building Tagging Basis . 75 4.9 Example . 76 4.10 Conclusion . 81 5 Financial Loss Models 82 5.1 Poisson Loss Model . 84 5.1.1 Discounted Losses due to Homogeneous Poisson Mainshock Process 86 5.1.2 Discounted Losses due to Nonhomogeneous Poisson Aftershock Process 89 5.2 Markov Loss Models . 92 5.2.1 Expected Total Discounted Losses due to Markov Mainshock Process 93 5.2.2 Expected Total Discounted Losses due to Markov Mainshock Process considering no more than 1 event in [0; tmax] . 96 5.2.3 Expected Total Discounted Losses due to Markov Mainshock Process with Repair . 97 5.2.4 Expected Total Discounted Losses due to Semi-Markov Mainshock Process . 98 5.2.5 Expected Total Undiscounted Losses due to Nonhomogeneous Markov Aftershock Process . 103 5.2.6 Expected Total Discounted Losses due to Nonhomogeneous Markov Aftershock Process . 107 5.3 Pre-Mainshock Loss Estimation . 109 vi 5.3.1 Formulation using Homogeneous Poisson Process for Mainshock Oc- currences . 111 5.3.2 Formulation using Renewal Process for Mainshock Occurrences . 112 5.4 Example . 113 5.5 Conclusion . 124 6 Seismic Decision Analysis 125 6.1 Decision Analysis using Decision Trees . 127 6.1.1 Example . 128 6.2 Decision Analysis allowing Damage-State Transitions . 142 6.3 Decision Analysis using Stochastic Dynamic Programming . 145 6.3.1 Methodology . 146 6.3.2 Example . 154 6.4 Conclusion . 161 7 Summary, Limitations and Future Work 162 7.1 Summary . 162 7.2 Conclusions . 164 7.3 Limitations . 165 7.4 Future Work . 167 vii List of Tables 5.1 Notations for Poisson model for a building in initial state i; Capital letters denote random variables . 86 5.2 Potential ¯nancial losses for each building damage state . 113 6.1 Potential ¯nancial losses for each building damage state . 131 6.2 Likelihood functions of \imperfect" engineer . 133 6.3 Case 1: Times in days after mainshock when the optimal decision changes from having evacuation to allowing re-occupancy. The individual life-safety constraint is enforced in this case without explicit minimization of ¯nancial losses. 155 6.4 Typical output of dynamic programming algorithm for the case where the individual life-safety constraint is not imposed, and where a cost per life saved of $2M is used. The optimal policy is shown as a function of elapsed days after the mainshock for all post-mainshock damage states. 158 6.5 Case 2: Times in days after mainshock when the optimal decision changes from having evacuation to allowing re-occupancy. The individual life-safety constraint is not enforced in this case. 158 6.6 Case 3: Times in days after mainshock when the optimal decision changes from having evacuation to allowing re-occupancy. The individual life-safety constraint is also enforced in this case. 160 viii List of Figures 1.1 A schematic plot of the aftershock environment. 2 1.2 Evacuated Occupants in Algeria Earthquake. 3 1.3 Pictures of a building which su®ered slight damage due to the 1999 Turkey Kocaeli mainshock that fully collapsed due to a smaller magnitude aftershock almost one month later. Photographs excerpted from USGS (2000). 10 1.4 Pictures of a column which was only slightly damaged due to the 2002 Italy Molise mainshock that su®ered severe spalling, bar buckling and a resid- ual vertical deformation at the top of the column due to an aftershock one day later. Photographs courtesy of Mucciarelli and Gallipoli, University of Basilicata, Italy and Dr. Paolo Bazzurro. 11 2.1 Schematic of site layout and linear aftershock zone. 24 2.2 Comparison of mainshock and aftershock site hazard curves (as functions of PGA), where aftershock hazard is evaluated at t = 7 days with T = 365 days for aftershocks equally likely to occur at any location on the linear aftershock zone and for aftershocks concentrated at the ends of the linear aftershock zone. The mainshock magnitude is assumed to be 7.0. 25 2.3 Mean number of aftershocks (as a function of elapsed time, t) with site PGA > 0.5g in speci¯ed durations T .......................... 26 2.4 Ratios of expected number of aftershocks resulting in site PGA > 0.5g for T = one week, one month, six months and one year to the expected number of aftershocks resulting in site PGA > 0.5g in one day, as a function of the elapsed time, t, of the ¯rst day in the duration of interest. 28 ix 2.5 Mean number of aftershocks (as a function of elapsed time t) with site PGA > 0.5g. The duration T is constant at one year in the ¯rst case (a), and the end time is constant at one year in the second case (b). 28 2.6 Aftershock hazard as a function of t for site PGA= 0.3g, 0.5g and 0.7g, and T = 365 days. The aftershock hazard is compared to the pre-mainshock hazard of exceeding the respective PGA values.
Load more

Recommended publications
  • Coulomb Stresses Imparted by the 25 March
    LETTER Earth Planets Space, 60, 1041–1046, 2008 Coulomb stresses imparted by the 25 March 2007 Mw=6.6 Noto-Hanto, Japan, earthquake explain its ‘butterfly’ distribution of aftershocks and suggest a heightened seismic hazard Shinji Toda Active Fault Research Center, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), site 7, 1-1-1 Higashi Tsukuba, Ibaraki 305-8567, Japan (Received June 26, 2007; Revised November 17, 2007; Accepted November 22, 2007; Online published November 7, 2008) The well-recorded aftershocks and well-determined source model of the Noto Hanto earthquake provide an excellent opportunity to examine earthquake triggering associated with a blind thrust event. The aftershock zone rapidly expanded into a ‘butterfly pattern’ predicted by static Coulomb stress transfer associated with thrust faulting. We found that abundant aftershocks occurred where the static Coulomb stress increased by more than 0.5 bars, while few shocks occurred in the stress shadow calculated to extend northwest and southeast of the Noto Hanto rupture. To explore the three-dimensional distribution of the observed aftershocks and the calculated stress imparted by the mainshock, we further resolved Coulomb stress changes on the nodal planes of all aftershocks for which focal mechanisms are available. About 75% of the possible faults associated with the moderate-sized aftershocks were calculated to have been brought closer to failure by the mainshock, with the correlation best for low apparent fault friction. Our interpretation is that most of the aftershocks struck on the steeply dipping source fault and on a conjugate northwest-dipping reverse fault contiguous with the source fault.
    [Show full text]
  • Intraplate Earthquakes in North China
    5 Intraplate earthquakes in North China mian liu, hui wang, jiyang ye, and cheng jia Abstract North China, or geologically the North China Block (NCB), is one of the most active intracontinental seismic regions in the world. More than 100 large (M > 6) earthquakes have occurred here since 23 BC, including the 1556 Huax- ian earthquake (M 8.3), the deadliest one in human history with a death toll of 830,000, and the 1976 Tangshan earthquake (M 7.8) which killed 250,000 people. The cause of active crustal deformation and earthquakes in North China remains uncertain. The NCB is part of the Archean Sino-Korean craton; ther- mal rejuvenation of the craton during the Mesozoic and early Cenozoic caused widespread extension and volcanism in the eastern part of the NCB. Today, this region is characterized by a thin lithosphere, low seismic velocity in the upper mantle, and a low and flat topography. The western part of the NCB consists of the Ordos Plateau, a relic of the craton with a thick lithosphere and little inter- nal deformation and seismicity, and the surrounding rift zones of concentrated earthquakes. The spatial pattern of the present-day crustal strain rates based on GPS data is comparable to that of the total seismic moment release over the past 2,000 years, but the comparison breaks down when using shorter time windows for seismic moment release. The Chinese catalog shows long-distance roaming of large earthquakes between widespread fault systems, such that no M ࣙ 7.0 events ruptured twice on the same fault segment during the past 2,000 years.
    [Show full text]
  • Seismic Rate Variations Prior to the 2010 Maule, Chile MW 8.8 Giant Megathrust Earthquake
    www.nature.com/scientificreports OPEN Seismic rate variations prior to the 2010 Maule, Chile MW 8.8 giant megathrust earthquake Benoit Derode1*, Raúl Madariaga1,2 & Jaime Campos1 The MW 8.8 Maule earthquake is the largest well-recorded megathrust earthquake reported in South America. It is known to have had very few foreshocks due to its locking degree, and a strong aftershock activity. We analyze seismic activity in the area of the 27 February 2010, MW 8.8 Maule earthquake at diferent time scales from 2000 to 2019. We diferentiate the seismicity located inside the coseismic rupture zone of the main shock from that located in the areas surrounding the rupture zone. Using an original spatial and temporal method of seismic comparison, we fnd that after a period of seismic activity, the rupture zone at the plate interface experienced a long-term seismic quiescence before the main shock. Furthermore, a few days before the main shock, a set of seismic bursts of foreshocks located within the highest coseismic displacement area is observed. We show that after the main shock, the seismic rate decelerates during a period of 3 years, until reaching its initial interseismic value. We conclude that this megathrust earthquake is the consequence of various preparation stages increasing the locking degree at the plate interface and following an irregular pattern of seismic activity at large and short time scales. Giant subduction earthquakes are the result of a long-term stress localization due to the relative movement of two adjacent plates. Before a large earthquake, the interface between plates is locked and concentrates the exter- nal forces, until the rock strength becomes insufcient, initiating the sudden rupture along the plate interface.
    [Show full text]
  • The 2018 Mw 7.5 Palu Earthquake: a Supershear Rupture Event Constrained by Insar and Broadband Regional Seismograms
    remote sensing Article The 2018 Mw 7.5 Palu Earthquake: A Supershear Rupture Event Constrained by InSAR and Broadband Regional Seismograms Jin Fang 1, Caijun Xu 1,2,3,* , Yangmao Wen 1,2,3 , Shuai Wang 1, Guangyu Xu 1, Yingwen Zhao 1 and Lei Yi 4,5 1 School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China; [email protected] (J.F.); [email protected] (Y.W.); [email protected] (S.W.); [email protected] (G.X.); [email protected] (Y.Z.) 2 Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan University, Wuhan 430079, China 3 Collaborative Innovation Center of Geospatial Technology, Wuhan University, Wuhan 430079, China 4 Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China; [email protected] 5 Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China * Correspondence: [email protected]; Tel.: +86-27-6877-8805 Received: 4 April 2019; Accepted: 29 May 2019; Published: 3 June 2019 Abstract: The 28 September 2018 Mw 7.5 Palu earthquake occurred at a triple junction zone where the Philippine Sea, Australian, and Sunda plates are convergent. Here, we utilized Advanced Land Observing Satellite-2 (ALOS-2) interferometry synthetic aperture radar (InSAR) data together with broadband regional seismograms to investigate the source geometry and rupture kinematics of this earthquake. Results showed that the 2018 Palu earthquake ruptured a fault plane with a relatively steep dip angle of ~85◦.
    [Show full text]
  • Foreshock Sequences and Short-Term Earthquake Predictability on East Pacific Rise Transform Faults
    NATURE 3377—9/3/2005—VBICKNELL—137936 articles Foreshock sequences and short-term earthquake predictability on East Pacific Rise transform faults Jeffrey J. McGuire1, Margaret S. Boettcher2 & Thomas H. Jordan3 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, and 2MIT-Woods Hole Oceanographic Institution Joint Program, Woods Hole, Massachusetts 02543-1541, USA 3Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-7042, USA ........................................................................................................................................................................................................................... East Pacific Rise transform faults are characterized by high slip rates (more than ten centimetres a year), predominately aseismic slip and maximum earthquake magnitudes of about 6.5. Using recordings from a hydroacoustic array deployed by the National Oceanic and Atmospheric Administration, we show here that East Pacific Rise transform faults also have a low number of aftershocks and high foreshock rates compared to continental strike-slip faults. The high ratio of foreshocks to aftershocks implies that such transform-fault seismicity cannot be explained by seismic triggering models in which there is no fundamental distinction between foreshocks, mainshocks and aftershocks. The foreshock sequences on East Pacific Rise transform faults can be used to predict (retrospectively) earthquakes of magnitude 5.4 or greater, in narrow spatial and temporal windows and with a high probability gain. The predictability of such transform earthquakes is consistent with a model in which slow slip transients trigger earthquakes, enrich their low-frequency radiation and accommodate much of the aseismic plate motion. On average, before large earthquakes occur, local seismicity rates support the inference of slow slip transients, but the subject remains show a significant increase1. In continental regions, where dense controversial23.
    [Show full text]
  • Hypocenter and Focal Mechanism Determination of the August 23, 2011 Virginia Earthquake Aftershock Sequence: Collaborative Research with VA Tech and Boston College
    Final Technical Report Award Numbers G13AP00044, G13AP00043 Hypocenter and Focal Mechanism Determination of the August 23, 2011 Virginia Earthquake Aftershock Sequence: Collaborative Research with VA Tech and Boston College Martin Chapman, John Ebel, Qimin Wu and Stephen Hilfiker Department of Geosciences Virginia Polytechnic Institute and State University 4044 Derring Hall Blacksburg, Virginia, 24061 (MC, QW) Department of Earth and Environmental Sciences Boston College Devlin Hall 213 140 Commonwealth Avenue Chestnut Hill, Massachusetts 02467 (JE, SH) Phone (Chapman): (540) 231-5036 Fax (Chapman): (540) 231-3386 Phone (Ebel): (617) 552-8300 Fax (Ebel): (617) 552-8388 Email: [email protected] (Chapman), [email protected] (Ebel), [email protected] (Wu), [email protected] (Hilfiker) Project Period: July 2013 - December, 2014 1 Abstract The aftershocks of the Mw 5.7, August 23, 2011 Mineral, Virginia, earthquake were recorded by 36 temporary stations installed by several institutions. We located 3,960 aftershocks from August 25, 2011 through December 31, 2011. A subset of 1,666 aftershocks resolves details of the hypocenter distribution. We determined 393 focal mechanism solutions. Aftershocks near the mainshock define a previously recognized tabular cluster with orientation similar to a mainshock nodal plane; other aftershocks occurred 10-20 kilometers to the northeast. Detailed relocation of events in the main tabular cluster, and hundreds of focal mechanisms, indicate that it is not a single extensive fault, but instead is comprised of at least three and probably many more faults with variable orientation. A large percentage of the aftershocks occurred in regions of positive Coulomb static stress change and approximately 80% of the focal mechanism nodal planes were brought closer to failure.
    [Show full text]
  • Qt88c3k67v.Pdf
    UC Berkeley UC Berkeley Previously Published Works Title Early aftershocks and afterslip surrounding the 2015 Mw 8.4 Illapel rupture Permalink https://escholarship.org/uc/item/88c3k67v Authors Huang, H Xu, W Meng, L et al. Publication Date 2017 DOI 10.1016/j.epsl.2016.09.055 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Early aftershocks and afterslip surrounding the 2015 Mw 8.4 Illapel rupture Author links open overlay panel HuiHuang a WenbinXu bc LingsenMeng a RolandBürgmann b Juan CarlosBaez d Show more https://doi.org/10.1016/j.epsl.2016.09.055 Get rights and content Highlights • Missing early aftershocks and repeaters are recovered by the matched- filtermethod. • Differential southward and northward expansion of early aftershocks are observed. • Repeaters and geodetic data reveal afterslip around the Illapel mainshock rupture. Abstract On 16 September 2015, the Mw 8.4 Illapel earthquake ruptured a section of the subduction thrust on the west coast of central Chile. The mainshock was followed by numerous aftershocks including some normal-faulting events near the trench. We apply a template matching approach to improve the completeness of early aftershocks within one month of the mainshock. To constrain the distribution of afterslip, we utilize repeating earthquakes among the aftershocks and perform a joint slip inversion of postseismic GPS and InSAR data. The results show that the aftershock zone abruptly expands to the south ∼14 h after the mainshock while growing relatively continuously to the north within the first day. The repeating earthquakes accompanying the early expansion suggest that aseismic afterslip on the subduction thrust surrounding the coseismic rupture is an important triggering mechanism of aftershocks in addition to stress transfer or poroelastic effects.
    [Show full text]
  • Common Dependence on Stress for the Two Fundamental Laws of Statistical Seismology
    Vol 462 | 3 December 2009 | doi:10.1038/nature08553 LETTERS Common dependence on stress for the two fundamental laws of statistical seismology Cle´ment Narteau1, Svetlana Byrdina1,2, Peter Shebalin1,3 & Danijel Schorlemmer4 Two of the long-standing relationships of statistical seismology their respective aftershocks (JMA). To eliminate swarms of seismicity are power laws: the Gutenberg–Richter relation1 describing the in the different volcanic areas of Japan, we also eliminate all after- earthquake frequency–magnitude distribution, and the Omori– shock sequences for which the geometric average of the times from Utsu law2 characterizing the temporal decay of aftershock rate their main shocks is larger than 4 hours. Thus, we remove spatial following a main shock. Recently, the effect of stress on the slope clusters of seismicity for which no clear aftershock decay rate exist. (the b value) of the earthquake frequency–magnitude distribution In order to avoid artefacts arising from overlapping records, we was determined3 by investigations of the faulting-style depen- focus on aftershock sequences produced by intermediate-magnitude dence of the b value. In a similar manner, we study here aftershock main shocks, disregarding the large ones. For the same reason, we sequences according to the faulting style of their main shocks. We consider only the larger aftershocks and we stack them according to show that the time delay before the onset of the power-law after- the main-shock time to compensate for the small number of events in shock decay rate (the c value) is on average shorter for thrust main each sequence. Practically, two ranges of magnitudeÂÃ have to be M M shocks than for normal fault earthquakes, taking intermediate definedÂÃ for main shocks and aftershocks, Mmin, Mmax and A A values for strike-slip events.
    [Show full text]
  • Mamuju–Majene
    Supendi et al. Earth, Planets and Space (2021) 73:106 https://doi.org/10.1186/s40623-021-01436-x EXPRESS LETTER Open Access Foreshock–mainshock–aftershock sequence analysis of the 14 January 2021 (Mw 6.2) Mamuju–Majene (West Sulawesi, Indonesia) earthquake Pepen Supendi1* , Mohamad Ramdhan1, Priyobudi1, Dimas Sianipar1, Adhi Wibowo1, Mohamad Taufk Gunawan1, Supriyanto Rohadi1, Nelly Florida Riama1, Daryono1, Bambang Setiyo Prayitno1, Jaya Murjaya1, Dwikorita Karnawati1, Irwan Meilano2, Nicholas Rawlinson3, Sri Widiyantoro4,5, Andri Dian Nugraha4, Gayatri Indah Marliyani6, Kadek Hendrawan Palgunadi7 and Emelda Meva Elsera8 Abstract We present here an analysis of the destructive Mw 6.2 earthquake sequence that took place on 14 January 2021 in Mamuju–Majene, West Sulawesi, Indonesia. Our relocated foreshocks, mainshock, and aftershocks and their focal mechanisms show that they occurred on two diferent fault planes, in which the foreshock perturbed the stress state of a nearby fault segment, causing the fault plane to subsequently rupture. The mainshock had relatively few after- shocks, an observation that is likely related to the kinematics of the fault rupture, which is relatively small in size and of short duration, thus indicating a high stress-drop earthquake rupture. The Coulomb stress change shows that areas to the northwest and southeast of the mainshock have increased stress, consistent with the observation that most aftershocks are in the northwest. Keywords: Mamuju–Majene, Earthquake, Relocation, Rupture, Stress-change Introduction mainshock from two of the nearest stations in Mamuju On January 14, 2021, a destructive earthquake (Mw 6.2) and Majene are 95.9 and 92.8 Gals, respectively, equiva- between Mamuju and Majene, West Sulawesi, Indonesia, lent to VI on the MMI scale (Additional fle 1: Figure S1).
    [Show full text]
  • Stress Relaxation Arrested the Mainshock Rupture of the 2016
    ARTICLE https://doi.org/10.1038/s43247-021-00231-6 OPEN Stress relaxation arrested the mainshock rupture of the 2016 Central Tottori earthquake ✉ Yoshihisa Iio 1 , Satoshi Matsumoto2, Yusuke Yamashita1, Shin’ichi Sakai3, Kazuhide Tomisaka1, Masayo Sawada1, Takashi Iidaka3, Takaya Iwasaki3, Megumi Kamizono2, Hiroshi Katao1, Aitaro Kato 3, Eiji Kurashimo3, Yoshiko Teguri4, Hiroo Tsuda5 & Takashi Ueno4 After a large earthquake, many small earthquakes, called aftershocks, ensue. Additional large earthquakes typically do not occur, despite the fact that the large static stress near the edges of the fault is expected to trigger further large earthquakes at these locations. Here we analyse ~10,000 highly accurate focal mechanism solutions of aftershocks of the 2016 Mw 1234567890():,; 6.2 Central Tottori earthquake in Japan. We determine the location of the horizontal edges of the mainshock fault relative to the aftershock hypocentres, with an accuracy of approximately 200 m. We find that aftershocks rarely occur near the horizontal edges and extensions of the fault. We propose that the mainshock rupture was arrested within areas characterised by substantial stress relaxation prior to the main earthquake. This stress relaxation along fault edges could explain why mainshocks are rarely followed by further large earthquakes. 1 Disaster Prevention Research Institute, Kyoto University, Gokasho Uji, Japan. 2 Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Fukuoka, Japan. 3 Earthquake Research Institute, University of
    [Show full text]
  • Stress Triggering in Thrust and Subduction Earthquakes and Stress
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, B02303, doi:10.1029/2003JB002607, 2004 Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike-slip faults Jian Lin Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA Ross S. Stein U.S. Geological Survey, Menlo Park, California, USA Received 30 May 2003; revised 24 October 2003; accepted 20 November 2003; published 3 February 2004. [1] We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks. Short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California the 1983 Mw = 6.7 Coalinga earthquake brought the subsequent 1983 Mw = 6.0 Nun˜ez and 1985 Mw = 6.0 Kettleman Hills ruptures 10 bars and 1 bar closer to Coulomb failure. The idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events, in agreement with findings of prior investigations. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust-faulting events on the periphery of the seismic rupture and its downdip extension.
    [Show full text]
  • Secondary Aftershocks and Their Importance for Aftershock Forecasting by Karen R
    Bulletin of the Seismological Society of America, Vol. 93, No. 4, pp. 1433–1448, August 2003 Secondary Aftershocks and Their Importance for Aftershock Forecasting by Karen R. Felzer, Rachel E. Abercrombie, and Go¨ran Ekstro¨m Abstract The potential locations of aftershocks, which can be large and damag- ing, are often forecast by calculating where the mainshock increased stress. We find, however, that the mainshock-induced stress field is often rapidly altered by after- shock-induced stresses. We find that the percentage of aftershocks that are secondary aftershocks, or aftershocks triggered by previous aftershocks, increases with time after the mainshock. If we only consider aftershock sequences in which all after- shocks are smaller than the mainshock, the percentage of aftershocks that are sec- ondary also increases with mainshock magnitude. Using the California earthquake catalog and Monte Carlo trials we estimate that on average more than 50% of after- shocks produced 8 or more days after M Ն5 mainshocks, and more than 50% of all aftershocks produced by M Ն7 mainshocks that have aftershock sequences lasting at least 15 days, are triggered by previous aftershocks. These results suggest that previous aftershock times and locations may be important predictors for new after- shocks. We find that for four large aftershock sequences in California, an updated forecast method using previous aftershock data (and neglecting mainshock-induced stress changes) can outperform forecasts made by calculating the static Coulomb stress change induced solely by the mainshock. Introduction It has long been observed that aftershocks may produce sequence. We also show that while the exact factors that their own aftershocks, commonly known as secondary af- determine aftershock location may be many and complex, tershocks (Richter, 1958).
    [Show full text]