DOCSLIB.ORG

EARTHQUAKE, AFTERSHOCKS Definition Introduction Scaling Laws for Aftershocks Causes of Aftershocks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
EARTHQUAKE, AFTERSHOCKS Definition Introduction Scaling Laws for Aftershocks Causes of Aftershocks 192 EARTHQUAKE, AFTERSHOCKS Earthquakes, Source Theory law, named for Fusakichi Omori’s observation of the Propagation of Elastic Waves: Fundamentals 1891 Nobi earthquake in Japan (Omori, 1894) and later Seismic Instrumentation modified by Utsu (1961): Surface Waves K nðtÞ¼ ðc þ tÞp EARTHQUAKE, AFTERSHOCKS where nðtÞ is the number of aftershocks by time t after the mainshock; K, p, and c are constants. The value of c is typ- Mian Liu1, Seth Stein2 ically positive close to zero, and p close to 1. Hence, the 1Department of Geological Sciences, University of number of aftershocks drops nearly hyperbolically with Missouri, Columbia, MO, USA time (Figure 1). The values of these constants are obtained 2Department of Earth and Planetary Sciences, by fitting to the data for each aftershock sequence. Northwestern University, Evanston, IL, USA It has been observed that the largest aftershock is usu- ally about 1 magnitude unit smaller than the mainshock, Definition independent of the mainshock magnitude. This is known as Båth’s law (Bath, 1965; Richter, 1958). However, Aftershocks. Smaller earthquakes following a large earth- because the data selection is retrospective and subjective, quake (the mainshock) in the same ruptured area. the size of aftershocks can vary substantially for different earthquake sequences. Introduction Like all earthquakes, the size distribution of aftershocks Earthquakes typically occur in sequences that may include follow the Gutenberg–Richter law (Gutenberg and foreshocks, the mainshock (the largest event or events), Richter, 1954): and aftershocks. Earthquake sequences without a clear mainshock are called swarms. log10NðMÞ¼a À bM Aftershocks generally refer to the smaller earthquakes where NðMÞ is the number of earthquakes of magnitude that follow a mainshock within certain spatial and tempo- M, a and b are constants. This relationship plots as ral windows. However, the criteria for choosing these win- a straight line with slope b, whose value, often referred dows are somewhat arbitrary. Typically, aftershocks are – ’ to as the b-value, is typically in the range of 0.8 1.2. For defined within an area around the mainshock s source b = 1, the number of earthquakes increases by a factor of region (i.e., the ruptured fault segment, which is about 10 for every unit drop. The b-value varies in time and 100 km long for a magnitude 7.0 earthquake). Most after- space even for the same fault. Some studies have shocks occur on the main rupture surface; hence, they are suggested that the b-value can be used as a stress indicator, often used to define the complex geometry of the rupture with lower b-values often associated with higher stresses plane. However, in many cases, especially for earthquakes (Schorlemmer et al., 2005). in subduction zones, the aftershock area increases signifi- cantly following the mainshock (Tajima and Kanamori, Causes of aftershocks 1985). Some aftershocks also occur off the main rupture Because most aftershocks occur on or near the rupture sur- surface. Distant earthquakes triggered by the mainshock’s face, they are thought to result from incomplete rupture seismic waves (see Artificial Water Reservoir Triggered and heterogeneous slip (e.g., Bullen and Bolt, 1947). This Earthquakes) may also be regarded as aftershocks notion is consistent with some case studies that found (Gomberg and Johnson, 2005). Temporally, aftershocks aftershocks concentrated around the perimeter of the rup- are defined as seismicity above the background activity ture zone or around asperities within the rupture zone following a main shock. This definition also leaves room where most of the coseismic slip occurred (Beroza, for ambiguity, as the background seismic activity can be 1991; Scholz, 2002). difficult to define in some places. The main causes of aftershocks are thought to include Aftershocks usually count for less than 5% of the total mainshock-induced changes of frictional properties of seismic energy release of the entire seismic sequence, so the fault zone and stress perturbations. Laboratory experi- they are secondary products (Scholz, 2002). However, ments indicate that frictional properties change with the besides their spatial and temporal relations to the duration of stationary contact and the instantaneous slid- mainshock, aftershocks are fundamentally no different ing velocity (Scholz, 2002). A constitutive relationship from other earthquakes and are recognized as aftershocks based on such results, known as the rate-and-state law only retrospectively (Helmstetter et al., 2003; Utsu, 2002). (Dieterich, 1979; Ruina, 1983), can explain the time- dependent changes of seismic rates that are consistent with Scaling laws for aftershocks the Omori’s law (Dieterich, 1994). Stress perturbations A large earthquake is usually followed by many smaller may arise from creep recovery of rocks in the immediate events (aftershocks); their occurrence rate decreases with areas of the fault (Benioff, 1951), viscous relaxation from time, typically following a pattern known as the Omori’s the lower crustal and upper mantle (Lieber and Braslau, EARTHQUAKE, AFTERSHOCKS 193 37°12′ 36°48′ a −122°24′−122°00′−121°36′−121°12′ 7 800 6 600 5 400 4 Magnitude 3 200 2 (shocks/yr) Seismicity rate 0 1980 1985 1990 1995 2000 2005 2010 1980 1985 1990 1995 2000 2005 2010 b Year c Year Earthquake, Aftershocks, Figure 1 (a) Topography and seismicity (circles, size proportional to magnitude) around the epicenter (star) of the 1989 Loma Prieta earthquake (Mw 6.9) on the San Andreas Fault. Green line marks the fault rupture; red lines enclose the spatial window for the aftershocks. (b) Earthquake occurrence between 1980 and 2010 within the spatial window. (c) Plot of seismicity showing the tÀ1 decay of aftershocks. 1965; Stein and Liu, 2009), and pore-elastic effects aftershocks are found to last 50–100 years. Within the (Scholz, 2002). In particular, the changes of the Coulomb stable continental interior, aftershock sequences may last static stress resulted from the mainshock have been shown hundreds of years or even longer (Stein and Liu, 2009). to cause spatial migration of seismicity and trigger earth- Such long aftershock sequences in continental interiors, quakes (Parsons, 2002; Stein, 1999). Other causes may where large earthquakes are infrequent and historic records include dynamic triggering (Gomberg and Johnson, are often incomplete, could bias hazard assessment. 2005) and pore fluid flow (Miller et al., 2004; Nur and Further complication may arise from the fact that earth- Booker, 1972). quakes tend to cluster in time and space, which is best shown in aftershock sequences. Studies of large shallow earthquakes in the world show that these large events often Aftershocks and earthquake hazard occur in pairs or groups (called doublets or multiplets); the Aftershocks can be large and damaging (e.g., Wiemer later events, which could be regarded as aftershocks, can et al., 2002). The durations of aftershock sequences for be bigger than the triggering event (the mainshock) plate-boundary earthquakes are typically around 10 years (Kagan and Jackson, 1999). Such clustering patterns are (Parsons, 2002)(Figure 1). However, aftershock sequences consistent with the emerging view that all earthquakes away from plate-boundary faults tend to last longer. In the can trigger their own earthquakes that in turn trigger more broadly deforming western United States, for example, quakes, and the triggered events may be bigger than the 194 EARTHQUAKE, FOCAL MECHANISM triggering event (Helmstetter et al., 2003; Ogata, 1998). Omori, F., 1894. On the aftershocks of earthquakes. Journal of Because the triggered events (the aftershocks) statistically the College of Science, Imperial University of Tokyo, 7, – follow the Omori’s law, statistical models can be devel- 111 200. Parsons, T., 2002. Global Omori law decay of triggered earth- oped to assess time-dependent probability of future dam- quakes: Large aftershocks outside the classical aftershock zone. aging earthquakes after each event (Gerstenberger et al., Journal of Geophysical Research, 107(B9), 2199, doi:10.1029/ 2005; Jones, 1985; Reasenberg and Jones, 1989). 2001JB000646. Reasenberg, P. A., and Jones, L. M., 1989. Earthquake hazard after a mainshock in California. Science, 243, 1173–1176. Summary Richter, C. F., 1958. Elementary Seismology. San Francisco: W. Aftershocks are smaller earthquakes following the H. Freeman. 768 pp. mainshock. They typically occur on or near the rupture Ruina, A., 1983. Slip instability and state variable friction laws. plane of the mainshock, resulting from changes of stress Journal of Geophysical Research, 88, 10359–10370. and frictional properties of the fault zone caused by the Scholz, C. H., 2002. The Mechanics of Earthquakes and Faulting. Cambridge/New York: Cambridge University Press. 471 pp. mainshock. The duration of aftershock sequences is typi- Schorlemmer, D., Wiemer, S., and Wyss, M., 2005. Variations in cally a few years for earthquakes at plate boundaries, but earthquake-size distribution across different stress regimes. can last much longer within stable continental interiors. Nature, 437, 539–542. Stein, R. S., 1999. The role of stress transfer in earthquake occur- rence. Nature, 402, 605–609. Bibliography Stein, S., and Liu, M., 2009. Long aftershock sequences within con- Bath, M., 1965. Lateral inhomogeneities in the upper mantle. tinents and implications for earthquake hazard assessment. Tectonophysics, 2, 483–514. Nature, 462,87–89. Benioff, H., 1951.
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]
  • Chapter 2 the Evolution of Seismic Monitoring Systems at the Hawaiian Volcano Observatory
    Characteristics of Hawaiian Volcanoes Editors: Michael P. Poland, Taeko Jane Takahashi, and Claire M. Landowski U.S. Geological Survey Professional Paper 1801, 2014 Chapter 2 The Evolution of Seismic Monitoring Systems at the Hawaiian Volcano Observatory By Paul G. Okubo1, Jennifer S. Nakata1, and Robert Y. Koyanagi1 Abstract the Island of Hawai‘i. Over the past century, thousands of sci- entific reports and articles have been published in connection In the century since the Hawaiian Volcano Observatory with Hawaiian volcanism, and an extensive bibliography has (HVO) put its first seismographs into operation at the edge of accumulated, including numerous discussions of the history of Kīlauea Volcano’s summit caldera, seismic monitoring at HVO HVO and its seismic monitoring operations, as well as research (now administered by the U.S. Geological Survey [USGS]) has results. From among these references, we point to Klein and evolved considerably. The HVO seismic network extends across Koyanagi (1980), Apple (1987), Eaton (1996), and Klein and the entire Island of Hawai‘i and is complemented by stations Wright (2000) for details of the early growth of HVO’s seismic installed and operated by monitoring partners in both the USGS network. In particular, the work of Klein and Wright stands and the National Oceanic and Atmospheric Administration. The out because their compilation uses newspaper accounts and seismic data stream that is available to HVO for its monitoring other reports of the effects of historical earthquakes to extend of volcanic and seismic activity in Hawai‘i, therefore, is built Hawai‘i’s detailed seismic history to nearly a century before from hundreds of data channels from a diverse collection of instrumental monitoring began at HVO.
    [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]
  • The Search for Empirical Formulae for the Aftershocks Descriptions of a Strong Earthquake A.V
    arXiv.org 2019 [physics.geo-ph] The search for empirical formulae for the aftershocks descriptions of a strong earthquake A.V. Guglielmi Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, ul. B. Gruzinskaya 10, Moscow, 123995 Russia, e-mail: [email protected] Abstract The paper is based on the report read by the author on October 24, 2018 at the meeting of the Scientific Council of the Institute of Earth Physics of the Russian Academy of Sciences. The report was dedicated to the 150th anniversary of the outstanding Japanese seismologist Fusakichi Omori. As is known, Omori established the first empirical law of the earthquakes physics, bearing his name. The Omori law states that the frequency of aftershocks on average decreases hyperbolically over the time. Three versions of Omori law are described briefly. The recent version allows to poses the inverse problem of the earthquake source, that “cools down” after the main shock. Keywords: earthquake source, aftershocks equation, deactivation coefficient, inverse problem Table of contents 1. Introduction 2. Three wordings of the Omori law 3. Inverse problem 4. Conclusion References 1. Introduction On October 24, 2018 at the meeting of the Academic Council of the Institute of Physics of the Earth RAS the author made a report dedicated to the 150th anniversary of the outstanding Japanese seismologist Fusakichi Omori (1868 – 1923). The presented paper summarizes the contents of this report. While still quite young, at the age of 26, Omori made an outstanding contribution to science, which has not lost its value these days [Davison, 1924; Guglielmi, 2017].
    [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]
  • Earthquake Resistant Design of Reinforced Concrete Buildings Past and Future Shunsuke Otani1
    Journal of Advanced Concrete Technology Vol. 2, No. 1, 3-24, February 2004 / Copyright © 2004 Japan Concrete Institute 3 Invited Paper Earthquake Resistant Design of Reinforced Concrete Buildings Past and Future Shunsuke Otani1 Received 9 September 2003, revised 26 November 2003 Abstract This paper briefly reviews the development of earthquake resistant design of buildings. Measurement of ground accel- eration started in the 1930s, and response calculation was made possible in the 1940s. Design response spectra were formulated in the late 1950s to 1960s. Non-linear response was introduced in seismic design in the 1960s and the capac- ity design concept was generally introduced in the 1970s for collapse safety. The damage statistics of reinforced con- crete buildings in the 1995 Kobe disaster demonstrated the improvement of building performance with the development of design methodology. Buildings designed and constructed using out-dated methodology should be upgraded. Per- formance-based engineering should be emphasized, especially for the protection of building functions following fre- quent earthquakes. 1. Introduction damage have been identified through the investigation of damages. Each damage case has provided important An earthquake, caused by a fault movement on the earth information regarding the improvement of design and surface, results in severe ground shaking leading to the construction practices and attention has been directed to damage and collapse of buildings and civil- the prevention of structural collapse to protect the oc- infra-structures, landslides in the case of loose slopes, cupants of building in the last century. and liquefaction of sandy soil. If an earthquake occurs Thank to the efforts of many pioneering researchers under the sea, the associated water movement causes and engineers, the state of the art in earthquake resistant high tidal waves called tsunamis.
    [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]