Hypocenter and Focal Mechanism Determination of the August 23, 2011 Virginia Earthquake Aftershock Sequence: Collaborative Research with VA Tech and Boston College
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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. -
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. -
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. -
The Growing Wealth of Aseismic Deformation Data: What's a Modeler to Model?
The Growing Wealth of Aseismic Deformation Data: What's a Modeler to Model? Evelyn Roeloffs U.S. Geological Survey Earthquake Hazards Team Vancouver, WA Topics • Pre-earthquake deformation-rate changes – Some credible examples • High-resolution crustal deformation observations – borehole strain – fluid pressure data • Aseismic processes linking mainshocks to aftershocks • Observations possibly related to dynamic triggering The Scientific Method • The “hypothesis-testing” stage is a bottleneck for earthquake research because data are hard to obtain • Modeling has a role in the hypothesis-building stage http://www.indiana.edu/~geol116/ Modeling needs to lead data collection • Compared to acquiring high resolution deformation data in the near field of large earthquakes, modeling is fast and inexpensive • So modeling should perhaps get ahead of reproducing observations • Or modeling could look harder at observations that are significant but controversial, and could explore a wider range of hypotheses Earthquakes can happen without detectable pre- earthquake changes e.g.Parkfield M6 2004 Deformation-Rate Changes before the Mw 6.6 Chuetsu earthquake, 23 October 2004 Ogata, JGR 2007 • Intraplate thrust earthquake, depth 11 km • GPS-detected rate changes about 3 years earlier – Moment of pre-slip approximately Mw 6.0 (1 div=1 cm) – deviations mostly in direction of coseismic displacement – not all consistent with pre-slip on the rupture plane Great Subduction Earthquakes with Evidence for Pre-Earthquake Aseismic Deformation-Rate Changes • Chile 1960, Mw9.2 – 20-30 m of slow interplate slip over a rupture zone 920+/-100 km long, starting 20 minutes prior to mainshock [Kanamori & Cipar (1974); Kanamori & Anderson (1975); Cifuentes & Silver (1989) ] – 33-hour foreshock sequence north of the mainshock, propagating toward the mainshock hypocenter at 86 km day-1 (Cifuentes, 1989) • Alaska 1964, Mw9.2 • Cascadia 1700, M9 Microfossils => Sea level rise before1964 Alaska M9.2 • 0.12± 0.13 m sea level rise at 4 sites between 1952 and 1964 Hamilton et al. -
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. -
Earthquake Measurements
EARTHQUAKE MEASUREMENTS The vibrations produced by earthquakes are detected, recorded, and measured by instruments call seismographs1. The zig-zag line made by a seismograph, called a "seismogram," reflects the changing intensity of the vibrations by responding to the motion of the ground surface beneath the instrument. From the data expressed in seismograms, scientists can determine the time, the epicenter, the focal depth, and the type of faulting of an earthquake and can estimate how much energy was released. Seismograph/Seismometer Earthquake recording instrument, seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free2. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is Seismograph what is recorded. Measuring Size of Earthquakes The size of an earthquake depends on the size of the fault and the amount of slip on the fault, but that’s not something scientists can simply measure with a measuring tape since faults are many kilometers deep beneath the earth’s surface. They use the seismogram recordings made on the seismographs at the surface of the earth to determine how large the earthquake was. A short wiggly line that doesn’t wiggle very much means a small earthquake, and a long wiggly line that wiggles a lot means a large earthquake2. The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip. -
Deep Dehydration As a Plausible Mechanism of the 2013 Mw 8.3 Sea of Okhotsk Deep-Focus Earthquake
ORIGINAL RESEARCH published: 04 August 2021 doi: 10.3389/feart.2021.521220 Deep Dehydration as a Plausible Mechanism of the 2013 Mw 8.3 Sea of Okhotsk Deep-Focus Earthquake Hao Zhang 1,2*, Suzan van der Lee 2, Craig R. Bina 2 and Zengxi Ge 3 1University of Utah Seismograph Stations, University of Utah, Salt Lake City, UT, United States, 2Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, United States, 3School of Earth and Space Sciences, Peking University, Beijing, China The rupture mechanisms of deep-focus (>300 km) earthquakes in subducting slabs of oceanic lithosphere are not well understood and different from brittle failure associated with shallow (<70 km) earthquakes. Here, we argue that dehydration embrittlement, often invoked as a mechanism for intermediate-depth earthquakes, is a plausible alternative model for this deep earthquake. Our argument is based upon the orientation and size of the plane that ruptured during the deep, 2013 Mw 8.3 Sea of Okhotsk earthquake, its rupture velocity and radiation efficiency, as well as diverse evidence of water subducting as deep as the transition zone and below. The rupture process of this earthquake has been inferred from back-projecting dual-band seismograms recorded at hundreds of seismic stations in North America and Europe, as well as by fitting P-wave trains recorded at dozens of Edited by: globally distributed stations. If our inferences are correct, the entirety of the subducting Sebastiano D’Amico, fi University of Malta, Malta Paci c lithosphere cannot be completely dry at deep, transition-zone depths, and other Reviewed by: deep-focus earthquakes may also be associated with deep dehydration reactions. -
Energy and Magnitude: a Historical Perspective
Pure Appl. Geophys. 176 (2019), 3815–3849 Ó 2018 Springer Nature Switzerland AG https://doi.org/10.1007/s00024-018-1994-7 Pure and Applied Geophysics Energy and Magnitude: A Historical Perspective 1 EMILE A. OKAL Abstract—We present a detailed historical review of early referred to as ‘‘Gutenberg [and Richter]’s energy– attempts to quantify seismic sources through a measure of the magnitude relation’’ features a slope of 1.5 which is energy radiated into seismic waves, in connection with the parallel development of the concept of magnitude. In particular, we explore not predicted a priori by simple physical arguments. the derivation of the widely quoted ‘‘Gutenberg–Richter energy– We will use Gutenberg and Richter’s (1956a) nota- magnitude relationship’’ tion, Q [their Eq. (16) p. 133], for the slope of log10 E versus magnitude [1.5 in (1)]. log10 E ¼ 1:5Ms þ 11:8 ð1Þ We are motivated by the fact that Eq. (1)istobe (E in ergs), and especially the origin of the value 1.5 for the slope. found nowhere in this exact form in any of the tra- By examining all of the relevant papers by Gutenberg and Richter, we note that estimates of this slope kept decreasing for more than ditional references in its support, which incidentally 20 years before Gutenberg’s sudden death, and that the value 1.5 were most probably copied from one referring pub- was obtained through the complex computation of an estimate of lication to the next. They consist of Gutenberg and the energy flux above the hypocenter, based on a number of assumptions and models lacking robustness in the context of Richter (1954)(Seismicity of the Earth), Gutenberg modern seismological theory. -
Large Intermediate-Depth Earthquakes and the Subduction Process
80 Physics ofthe Earth and Planetary Interiors, 53 (1988) 80—166 Elsevier Science Publishers By., Amsterdam — Printed in The Netherlands Large intermediate-depth earthquakes and the subduction process Luciana Astiz ~, Thorne Lay 2 and Hiroo Kanamori ~ ‘Seismological Laboratory, California Institute of Technology, Pasadena, CA (U.S.A.) 2 Department of Geological Sciences, University ofMichigan, Ann Arbor, MI (USA.) (Received September 22, 1987; accepted October 21, 1987) Astiz, L., Lay, T. and Kanamori, H., 1988. Large intermediate-depth earthquakes and the subduction process. Phys. Earth Planet. Inter., 53: 80—166. This study provides an overview of intermediate-depth earthquake phenomena, placing emphasis on the larger, tectonically significant events, and exploring the relation of intermediate-depth earthquakes to shallower seismicity. Especially, we examine whether intermediate-depth events reflect the state of interplate coupling at subduction zones. and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes. Historic record of large intraplate earthquakes (m B 7.0) in this century shows that the New Hebrides and Tonga subduction zones have the largest number of large intraplate events. Regions associated with bends in the subducted lithosphere also have many large events (e.g. Altiplano and New Ireland). We compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with M> 6 and depth between 40 and 200 km. The final catalog includes 335 events with 47 new focal mechanisms, and is probably complete for earthquakes with mB 6.5. For events with M 6.5, nearly 48% of the events had no aftershocks and only 15% of the events had more than five aftershocks within one week of the mainshock. -
Phantom Earthquakes
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Zagros \phantom earthquakes" reassessed | the interplay of seismicity and deep salt flow in the Simply Folded Belt? Edwin Nissen,1 James Jackson,2 Salman Jahani,3 and Mohammad Tatar4 Abstract. Unravelling the contributions of mainshock slip, aftershocks, aseismic after- slip and postseismic relaxation to the deformation observed in earthquake sequences height- ens our understanding of crustal rheology, triggering phenomena and seismic hazard. Here, we revisit two recent earthquakes in the Zagros mountains (Iran) which exhibited un- usual and contentious after-effects. The Mw ∼6 earthquakes at Qeshm (2005) and Fin (2006) are both associated with large InSAR signals, consistent with slip on steep re- verse faults in carbonate rocks of the middle sedimentary cover, but small aftershocks detected with local seismic networks were concentrated at significantly greater depths. This discrepancy can be interpreted in one of two ways: either (1) there is a genuine ver- tical separation between mainshock and aftershocks, reflecting a complex stress state near the basement{cover interface; or (2) the aftershocks delimit the mainshock slip and the InSAR signals were caused by shallow, up-dip afterslip (\phantom earthquakes") with very similar magnitudes, mechanisms and geographical positions as the original earth- quakes. Here, we show that mainshock centroid depths obtained from body-waveform modelling | which in this instance is the only method that can reveal for certain the depth at which seismic slip was centered | strongly support the first interpretation. At Qeshm, microseismic aftershock depths are centered at the level of the Hormuz Forma- tion, an Infracambrian sequence of intercalated evaporitic and non-evaporitic sediments. -
What Is an Earthquake?
A Violent Pulse: Earthquakes Chapter 8 part 2 Earthquakes and the Earth’s Interior What is an Earthquake? Seismicity • ‘Earth shaking caused by a rapid release of energy.’ • Seismicity (‘quake or shake) cause by… – Energy buildup due tectonic – Motion along a newly formed crustal fracture (or, stresses. fault). – Cause rocks to break. – Motion on an existing fault. – Energy moves outward as an expanding sphere of – A sudden change in mineral structure. waves. – Inflation of a – This waveform energy can magma chamber. be measured around the globe. – Volcanic eruption. • Earthquakes destroy – Giant landslides. buildings and kill people. – Meteorite impacts. – 3.5 million deaths in the last 2000 years. – Nuclear detonations. • Earthquakes are common. Faults and Earthquakes Earthquake Concepts • Focus (or Hypocenter) - The place within Earth where • Most earthquakes occur along faults. earthquake waves originate. – Faults are breaks or fractures in the crust… – Usually occurs on a fault surface. – Across which motion has occurred. – Earthquake waves expand outward from the • Over geologic time, faulting produces much change. hypocenter. • The amount of movement is termed displacement. • Epicenter – Land surface above the focus pocenter. • Displacement is also called… – Offset, or – Slip • Markers may reveal the amount of offset. Fence separated by fault 1 Faults and Fault Motion Fault Types • Faults are like planar breaks in blocks of crust. • Fault type based on relative block motion. • Most faults slope (although some are vertical). – Normal fault • On a sloping fault, crustal blocks are classified as: • Hanging wall moves down. – Footwall (block • Result from extension (stretching). below the fault). – Hanging wall – Reverse fault (block above • Hanging wall moves up. -
Nissen-Etal-2010-EPS
Earth and Planetary Science Letters 296 (2010) 181–194 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl The vertical separation of mainshock rupture and microseismicity at Qeshm island in the Zagros fold-and-thrust belt, Iran E. Nissen a,⁎, F. Yamini-Fard b, M. Tatar b, A. Gholamzadeh b,1, E. Bergman c, J.R. Elliott d, J.A. Jackson a, B. Parsons d a COMET, Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK b International Institute of Earthquake Engineering and Seismology, PO Box 19395-3913, Tehran, Iran c Department of Physics, University of Colorado, Boulder, CO 80309-0390, USA d COMET, Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK article info abstract Article history: We investigate the depth and geometry of faulting within a cluster of buried, reverse faulting earthquakes Received 11 January 2010 that struck Qeshm island, in the Zagros fold-and-thrust belt, over a four year period between November 2005 Received in revised form 24 March 2010 and July 2009. Of particular interest is our observation that there was a vertical separation between the Accepted 24 April 2010 largest two earthquakes (M 5.8 and 5.9), which ruptured the lower parts of a ∼10-km thick sedimentary Available online 9 June 2010 w cover, and microseismicity recorded by a local network after the first, Mw 5.8 event, which was concentrated – — Editor: T.M. Harrison within the underlying basement at depths of 10 20 km.