Contribution of Slow Earthquake Study for Assessing the Occurrence Potential of Megathrust Earthquakes

Total Page:16

File Type:pdf, Size:1020Kb

Contribution of Slow Earthquake Study for Assessing the Occurrence Potential of Megathrust Earthquakes Contribution of Slow Earthquake Study for Assessing the Occurrence Potential of Megathrust Earthquakes Review: Contribution of Slow Earthquake Study for Assessing the Occurrence Potential of Megathrust Earthquakes Kazushige Obara Earthquake Research Institute, The University of Tokyo 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan E-mail: [email protected] [Received February 17, 2014; accepted May 12, 2014] Studies of slow earthquakes during the last decade nomena, may be related to the stress regimes that cause have suggested a relationship between various types megathrust earthquakes, as the source regions of the two of earthquakes occurring at the interface between types of earthquakes are adjacent to one another. subducting oceanic plates and overlying continental Slow earthquakes can be broadly classified into seismic plates. Such a relationship has been postulated for and geodetic phenomena. For example, in 1992, an after- slow earthquakes, which are distributed between the slip event (in which the slip deficit accumulating adjacent stable sliding zone and the locked zone, and megath- to a large earthquake source fault is released) followed rust earthquakes, which are located in the locked by a magnitude (M) 6.9 earthquake off northern Honshu, zone. The adjacency of the respective sources of slow Japan, was first reported by Kawasaki et al. (1995) [1] and megathrust earthquakes suggests expected inter- as a geodetic slow earthquake (Fig. 2). The development actions between these two types of earthquakes. Ob- of GPS observation networks since the 1990s has enabled served interactions between different types of slow not only the detection of some afterslip events, but also earthquakes located at neighbor area suggest a com- the discovery of slow slip events (SSEs), in which small mon triggering mechanism in the seismogenic zone. amounts of crustal deformation occur spontaneously. Af- Also, it is expected that stress accumulations in the ter the construction of the GPS network GEONET, op- locked zone should influence stress regimes in sur- erated by the Geospatial Information Authority of Japan rounding regions; thus, slow earthquake activity in the (GSI) (Sagiya, 2004 [2]), an SSE lasting for about one stable sliding zone may change in response to stress year was detected in 1997 in the Bungo Channel between build-up in the locked zone. Numerical simulations Kyushu and Shikoku islands, southwestern Japan (Fig. 2). reproducing both megathrust and slow earthquakes Hirose et al. (1999) [3] estimated that the SSE event was show a shortening of the recurrence interval between generated by a thrusttype focal mechanism located on the slow earthquake episodes leading up to the occurrence downdip side of the Nankai earthquake seismogenic zone. of a megathrust earthquake. Similarities between the In the Tokai region, central Japan, similar SSEs were de- activities of slow and megathrust earthquakes, such as tected between late 2000 and 2005 (e.g., Ozawa et al., those related to periodicity and patterns of multiseg- 2002 [4]; Miyazaki et al., 2006 [5]). The Tokai SSE was ment ruptures, are useful for understanding megath- of interest because during the initial stage, the SSE oc- rust earthquakes, particularly given the higher fre- curred along the downdip part of the slab interface neigh- quency of occurrence of slow earthquakes. From this boring the source area of an anticipated Tokai earthquake. perspective, the continuous and accurate monitoring Similarly, SSEs with large magnitudes (M7) and long du- of slow earthquake activity is important for evaluating rations (months to years) have been detected in other sub- the occurrence potential of megathrust earthquakes. duction zones, for example in Alaska (e.g., Ohta et al., 2006 [6]) and in Mexico (e.g., Vergnolle et al., 2010 [7]) Keywords: slow earthquake, nonvolcanic tremor, slow (Fig. 3). slip, subduction zone, megathrust earthquake In the Cascadia subduction zone, along the western coast of North America, a significant SSE was discovered by a network of densely distributed GPS sites (Dragert 1. Introduction et al., 2001 [8]) (Fig. 3). This SSE (Mw6.7) was a reverse faulting event occurring on the interface of the deeper part Slow earthquakes, which are characterized by a wide from the megathrust seismogenic zone along the subduct- spectral range, and megathrust earthquakes both occur in ing plate interface. The duration of the SSE of weeks was subduction zones, along the interface between oceanic much shorter than those of the SSEs in Japan, Alaska, and and overlying plates (Fig. 1). The source of slow earth- Mexico described above. To discriminate SSEs based on quakes is in the transition zone between the locked and their durations, events such as the SSE in Cascadia are re- stable sliding zones. Therefore, the occurrence of slow ferred to as short-term SSEs, while SSEs with durations earthquakes, which are considered as transitional phe- of months to years (such as those in the Bungo Channel, Journal of Disaster Research Vol.9 No.3, 2014 317 Obara, K. Near Downdip side Nankai Trough Characteristic time (tc) Sensor Network Long-term slow slip event GPS GSI 100day (tc:0.5~5years) GEONET Short-term slow slip event 1day Tiltmeter (tc:2~6days) 1000sec Deep very low frequency Tiltmeter NIED Earthquake䠄VLF䠅 (tc:20sec䠅 Hi-net Shallow very low 10sec frequency earthquake Deep low frequency tremor Short-period (S-VLF) (tc:10sec䠅 0.1sec (tc:1.5~5Hz) seismometer Accretionary prism Nankai Trough Long-term SSE Episodic Tremor and Slip Short-term SSE S-VLF VLF Tremor Fig. 1. Cross sectional schematic illustration of slow earthquakes in southwest Japan. On the top panel, the difference in characteristic time of each slow earthquake is shown. On the right side of the top panel, adequate sensor and observation network for each slow earthquake are indicated. Tokai, Alaska, and Mexico) are referred to as long-term SSEs. Interestingly, the short-term SSE in Cascadia was Afterslip characterized by an along-strike migration of the source Long-term SSE location at a speed of several km per day. After the dis- covery of the Cascadia SSE, Miller et al. (2002) [9] found Boso-type SSE 1 that it recurred at an interval of about 14 months. There- Shallow VLF Tokachi-oki fore, this SSE is interpreted as a stickslip phenomenon ETS(Deep VLF, tremor, 11 Short-term SSE) occurring on the downdip side of the megathrust seis- 2 Sanriku-oki mogenic zone, which is estimated to have ruptured in Tohoku SSE AD 1700 based on historical descriptions of tsunami in 15 Japan (Satake et al., 2003 [10]) (Fig. 4). 3 Miyagi-oki A nonvolcanic tremor was the first seismic slow earth- 4 quake to be recorded in southwestern Japan (Obara, Fukushima-oki 2002 [11]; Obara and Shiomi, 2009 [12]) (Figs. 1 and 2) Tokai 10 14 based on the analysis of Hi-net operated by National Re- Bungo Cha. 6 search Institute for Earth Science and Disaster Prevention 14 Boso 14 (NIED) (Okada et al., 2004 [13]; Obara et al., 2005 [14]). 7 12 12 8 12 12 The tremor was distributed along a belt-shaped zone on 5 13 9 the downdip side of the seismogenic zone of the Nankai 12 Trough megathrust earthquake, parallel to the strike of the Hyuga-nada subducting Philippine Sea Plate. The tremor source lo- cation usually migrated along strike at a velocity of ap- Fig. 2. Distribution of slow earthquakes in Japan. proximately 10 km/day. Based on the similarity of the Afterslip: 1, Miyazaki et al. (2004) [16]; 2, Kawasaki et short-term SSEs in Cascadia and the tremor in south- al. (1995) [1]; 3, Miura et al. (2006) [17]; 4, Suito et al. western Japan, with respect to their locations relative to (2011) [18]; 5, Yagi and Kikuchi (2003) [19], Long-term the seismogenic zone and to their migration properties, SSE: 6, Miyazaki et al. (2006) [5]; 7, Kobayashi (2012) [20]; Rogers and Dragert (2003) [15] searched for a seismic 8, Hirose et al. (1999) [3]; 9, Yarai and Ozawa (2013) [21], tremor during the occurrence period of the SSEs in Cas- Boso-type SSE: 10, Hirose et al. (2012) [22], Shallow VLF cadia and discovered a coupled phenomenon composed earthquake: 11, Asano et al. (2008) [23]; 12, Obara and Ito of a geodetic SSE and a seismic tremor, referred to as (2005) [24]; 13, Hirose et al. (2010) [25], ETS: 14, Obara et episodic tremor and slip (ETS) (Fig. 4). A coupling phe- al. (2004) [26], Ito et al. (2007) [27], Tohoku SSE: 15, Kato nomenon that includes both short-term SSE and tremor et al. (2012) [28], Ito et al. (2013) [29]. 318 Journal of Disaster Research Vol.9 No.3, 2014 Contribution of Slow Earthquake Study for Assessing the Occurrence Potential of Megathrust Earthquakes ETS(Episodic tremor and slip) Alaska Deep VLF earthquake 21 14 9 60N Aleutian Queen Charlotte Fault Ambient tremor without SSE 9 (including triggered tremor) 2 Cascadia 8 San Andreas Fault Triggered tremor only Japan 30N Mexico Taiwan 4 19 20 Long-term SSE 13 9 10 1 31517 Haiti Boso-type shallow SSE 22 Costa Rica 0 Shallow VLF earthquake 12 7 18 Tremor excited by SSE 30S Shallow VLF excited by SSE New Zealand 6 Southern Chile 11 5 16 60S 0 60E 120E 180W 120W 60W Fig. 3. World-wide distribution of various types of slow earthquakes. ETS: 1, Obara et al. (2004) [26], Maeda and Obara (2009) [30]; 2, Rogers and Dragert (2003) [15], Deep VLF earthquake: 3, Ito et al. (2007) [27], Ambient tremor: 4, Peng and Chao (2008) [31], Chao et al. (2013) [32]; 5, Ide (2012) [33], Kim et al. (2011) [34]; 6, Gallego et al. (2013) [35]; 7, Brown et al. (2009) [36]; 8, Nadeau and Dolenc (2005) [37], Triggered tremor: 9, Chao et al.
Recommended publications
  • 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]
  • 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]
  • Slow Slip Event on the Southern San Andreas Fault Triggered by the 2017 Mw8.2 Chiapas (Mexico) Earthquake That Occurred 3,000 Km Away
    RESEARCH ARTICLE Slow Slip Event On the Southern San Andreas Fault 10.1029/2018JB016765 Triggered by the 2017 Mw8.2 Chiapas (Mexico) Key Points: Earthquake • We present geodetic and geologic observations of slow slip on the 1,2 1 1,3 1 southern SAF triggered by the 2017 Ekaterina Tymofyeyeva , Yuri Fialko , Junle Jiang , Xiaohua Xu , Chiapas (Mexico) earthquake David Sandwell1 , Roger Bilham4 , Thomas K. Rockwell5 , Chelsea Blanton5 , • The slow slip event produced surface 5 5 6 offsets on the order of 5–10 mm, with Faith Burkett ,Allen Gontz , and Shahram Moafipoor significant variations along strike 1 • We interpret the observed complexity Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, in shallow fault slip in the context of La Jolla, CA, USA, 2Now at Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA, 3Now at rate-and-state friction models Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA, 4CIRES and Geological Sciences, University of Colorado, Boulder, CO, USA, 5Department of Geological Sciences, San Diego State University, San Diego, 6 Supporting Information: CA, USA, Geodetics Inc., San Diego, CA, USA • Supporting Information S1 Abstract Observations of shallow fault creep reveal increasingly complex time-dependent slip Correspondence to: histories that include quasi-steady creep and triggered as well as spontaneous accelerated slip events. Here E. Tymofyeyeva, [email protected] we report a recent slow slip event on the southern San Andreas fault triggered by the 2017 Mw8.2 Chiapas (Mexico) earthquake that occurred 3,000 km away. Geodetic and geologic observations indicate that surface slip on the order of 10 mm occurred on a 40-km-long section of the southern San Andreas fault Citation: Tymofyeyeva, E., Fialko, Y., Jiang, J., between the Mecca Hills and Bombay Beach, starting minutes after the Chiapas earthquake and Xu, X., Sandwell, D., Bilham, R., et al.
    [Show full text]
  • The Megathrust Earthquake Cycle
    Ocean. A little less than four years later, a similar-sized earthquake strikes the Prince William Sound area of Alaska producing a tsunami that ravages Alaska and the west coast of North America. At the time, it was clear Not My Fault: The megathrust these were very large quakes, registering 8.6 and 8.5 on earthquake cycle the Surface Wave magnitude scale, the variant of the Lori Dengler/For the Times-Standard Richter scale that was in use at the time. But only after Posted: May 24, 2017 theresearch of two more Reid award winners Aki and Kanamori (whose work would replace the Richter scale The Seismological Society of America is the world’s with seismic moment and moment magnitude) would largest organization dedicated to the study of the true size of these earthquakes Become clear. When earthquakes and their impacts on humans. The recalculated in the 70s, 1964 Alaska was upped to 9.2 Society’s highest honor is the Henry F. Reid Award and 1960 Chile Became a whopping 9.5, the largest recognizes the work that has done the most to the magnitude earthquake ever recorded on a seismograph. transform the discipline. This year’s recipient is George Plafker for his studies of great suBduction zone Both of these earthquakes occurred before plate earthquakes. tectonics, the grand unifying theory of how the outer part of the earth works, was well known or accepted. In I mentioned Dr. Plafker in my last column as a pioneer of the sixties, many earth scientists Believed great post earthquake/tsunami reconnaissance.
    [Show full text]
  • Fully-Coupled Simulations of Megathrust Earthquakes and Tsunamis in the Japan Trench, Nankai Trough, and Cascadia Subduction Zone
    Noname manuscript No. (will be inserted by the editor) Fully-coupled simulations of megathrust earthquakes and tsunamis in the Japan Trench, Nankai Trough, and Cascadia Subduction Zone Gabriel C. Lotto · Tamara N. Jeppson · Eric M. Dunham Abstract Subduction zone earthquakes can pro- strate that horizontal seafloor displacement is a duce significant seafloor deformation and devas- major contributor to tsunami generation in all sub- tating tsunamis. Real subduction zones display re- duction zones studied. We document how the non- markable diversity in fault geometry and struc- hydrostatic response of the ocean at short wave- ture, and accordingly exhibit a variety of styles lengths smooths the initial tsunami source relative of earthquake rupture and tsunamigenic behavior. to commonly used approach for setting tsunami We perform fully-coupled earthquake and tsunami initial conditions. Finally, we determine self-consistent simulations for three subduction zones: the Japan tsunami initial conditions by isolating tsunami waves Trench, the Nankai Trough, and the Cascadia Sub- from seismic and acoustic waves at a final sim- duction Zone. We use data from seismic surveys, ulation time and backpropagating them to their drilling expeditions, and laboratory experiments initial state using an adjoint method. We find no to construct detailed 2D models of the subduc- evidence to support claims that horizontal momen- tion zones with realistic geometry, structure, fric- tum transfer from the solid Earth to the ocean is tion, and prestress. Greater prestress and rate-and- important in tsunami generation. state friction parameters that are more velocity- weakening generally lead to enhanced slip, seafloor Keywords tsunami; megathrust earthquake; deformation, and tsunami amplitude.
    [Show full text]
  • Drilling Into Shallow Interplate Thrust Zone for Understanding of Irregular Rupturing of Megathrust
    Drilling into shallow interplate thrust zone for understanding of irregular rupturing of megathrust Ryota Hino (Tohoku University) * abstract It is generally conceived that the shallowest portion of the megathrsut fault is completely aseismic and allow stable sliding during the interseismic period. However, anomalous tsunami earthquakes sporadically happen in this area, causing disproportionally large tsunami as compared to the radiated seismic energy, release large displacement at the plate boundary. It has not been well understood why and how such the anomalous earthquake occurs irregularly. Also in the rupture propagation of gigantic (M>9) earthquakes involving simultaneous rupturing of multiple asperities, the aseismic plate boundary seems to play an important role. Therefore, the mechanical properties of the most trenchward zone of the subudction plate boundary are very important for understanding mechanisms generating catastrophic earthquakes. I propose here to make long-term monitoring in deep boreholes drilled the shallowest portion of the megathrust fault to clarify how deform this area in the interseismic period. Downhole logging and seismic profiling will provide the answer to the cause of the anomalous rupture process by revealing the internal structure of the fault zone. * Research center for prediction of earthquakes and volcanic eruption Graduate School of Science, Tohoku University [email protected] 1. Introduction The occurrence of the 2004 Sumatra-Andaman earthquake (M9.1) showed that an interplate earthquake which ruptures almost entire part of a subduction system can occur, although we only know recurrence history of thrust earthquakes with sizes of M~8 in the system. Recent paleoseismological studies have revealed the occurrence of gigathrust earthquakes, much larger than M8 class megathrust earthquakes, in other subduction zones where only megathrust earthquakes have been known to occur.
    [Show full text]
  • Laboratory Earthquake Forecasting: a Machine Learning Competition PERSPECTIVE Paul A
    PERSPECTIVE Laboratory earthquake forecasting: A machine learning competition PERSPECTIVE Paul A. Johnsona,1,2, Bertrand Rouet-Leduca,1, Laura J. Pyrak-Nolteb,c,d,1, Gregory C. Berozae, Chris J. Maronef,g, Claudia Hulberth, Addison Howardi, Philipp Singerj,3, Dmitry Gordeevj,3, Dimosthenis Karaflosk,3, Corey J. Levinsonl,3, Pascal Pfeifferm,3, Kin Ming Pukn,3, and Walter Readei Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved November 28, 2020 (received for review August 3, 2020) Earthquake prediction, the long-sought holy grail of earthquake science, continues to confound Earth scientists. Could we make advances by crowdsourcing, drawing from the vast knowledge and creativity of the machine learning (ML) community? We used Google’s ML competition platform, Kaggle, to engage the worldwide ML community with a competition to develop and improve data analysis approaches on a forecasting problem that uses laboratory earthquake data. The competitors were tasked with predicting the time remaining before the next earthquake of successive laboratory quake events, based on only a small portion of the laboratory seismic data. The more than 4,500 participating teams created and shared more than 400 computer programs in openly accessible notebooks. Complementing the now well-known features of seismic data that map to fault criticality in the laboratory, the winning teams employed unex- pected strategies based on rescaling failure times as a fraction of the seismic cycle and comparing input distribution of training and testing data. In addition to yielding scientific insights into fault processes in the laboratory and their relation with the evolution of the statistical properties of the associated seismic data, the competition serves as a pedagogical tool for teaching ML in geophysics.
    [Show full text]
  • Fault Stressing in the Overriding Plate Due to Megathrust Coupling Along the Nankai Trough, Japan
    EGU2020-18393 https://doi.org/10.5194/egusphere-egu2020-18393 EGU General Assembly 2020 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Fault stressing in the overriding plate due to megathrust coupling along the Nankai trough, Japan Akinori Hashima1, Hiroshi Sato1, Tatsuya Ishiyama1, Andrew Freed2, and Thorsten Becker3 1Earthquake Research Institute, University of Tokyo, Tokyo, Japan 2Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, USA 3Jackson School of Geosciences, The University of Texas at Austin, Austin, USA The Nankai trough has hosted ~M8 interplate earthquakes with the interval of 100-200 years. The crustal activity in southwest (SW) Japan in the overriding plate was relatively quiet after the last coupled megathrust ruptures occurred in 1944 and 1946. In the recent 20 years, however, SW Japan has experienced ~M7 earthquakes such as the 2016 Kumamoto earthquake. Similar activation of crustal earthquakes in the later stage of the megathrust earthquake cycles can be found in the historical earthquake occurrence based on paleographical studies. Such a change cannot be resolved by the probabilistic approaches, which usually rely on paleo-seismological data on longer timescales. Here, we show a deterministic way to quantify the current stressing state on the source faults due to megathrust coupling at the Nankai trough, making use of the data captured by the dense, modern geodetic network in Japan. We constructed a 3-D finite element model (FEM) around the Japanese islands including the viscoelastic feature in the asthenosphere. The geometry of plate boundary on the Philippine Sea slab is based on earthquake distributions determined by the previous studies.
    [Show full text]
  • Distribution of Discrete Seismic Asperities and Aseismic Slip Along the Ecuadorian Megathrust ∗ M
    Earth and Planetary Science Letters 400 (2014) 292–301 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Distribution of discrete seismic asperities and aseismic slip along the Ecuadorian megathrust ∗ M. Chlieh a, , P.A. Mothes b, J.-M. Nocquet a, P. Jarrin b, P. Charvis a, D. Cisneros c, Y. Font a, J.-Y. Collot a, J.-C. Villegas-Lanza d, F. Rolandone e, M. Vallée f, M. Regnier a, M. Segovia b, X. Martin a, H. Yepes b a Géoazur, Université Nice Sophia Antipolis, IRD, CNRS, OCA, Nice, France b Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador c Instituto Geográfico Militar, Quito, Ecuador d Instituto Geofísico del Perú, Lima, Peru e Université Pierre et Marie Curie, Paris, France f Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, UMR 7154 CNRS, 75005 Paris, France a r t i c l e i n f o a b s t r a c t Article history: A dense GPS network deployed in Ecuador reveals a highly heterogeneous pattern of interseismic Received 16 January 2014 coupling confined in the first 35 km depth of the contact between the subducting oceanic Nazca Received in revised form 11 May 2014 plate and the North Andean Sliver. Interseismic models indicate that the coupling is weak and very Accepted 14 May 2014 shallow (0–15 km) in south Ecuador and increases northward, with maximum found in the rupture Available online xxxx areas of large (Mw > 7.0) megathrust earthquakes that occurred during the 20th century.
    [Show full text]
  • 180-Million-Year-Old Rocks Lend Insight Into Earth's Most Powerful Earthquakes 19 December 2016
    180-million-year-old rocks lend insight into Earth's most powerful earthquakes 19 December 2016 The raggedness of the ocean floors could be the However, there are many regions across the world, key to triggering some of the Earth's most powerful including in the 'Ring of Fire', where scientists earthquakes, scientists from Cardiff University would expect megathrust earthquakes to occur, but have discovered. they don't. In a new study published today in Nature The new research appears to have solved this Geoscience the team, also from Utrecht University, conundrum and therefore propose an explanation suggest that large bumps and mounds on the sea as to what triggers giant earthquakes. The team floor could be the trigger point that causes the arrived at their conclusions by examining rocks crust in the Earth's oceans to drastically slip that, through erosion and tectonic uplift, have been beneath the crust on the continent and generate a carried to the Earth's surface from depths of giant earthquake. 15-20km in an extinct fault zone in New Zealand that was once active around 180 million years ago. By studying exposed rocks from a 180-million-year- old extinct fault zone in New Zealand, the The team found that the rocks in the fault zone can researchers have shown, for the first time, that the be tens to hundreds of metres thick and can act as extremely thick oceanic and continental tectonic a sponge to soak up the pressure that builds as two plates can slide against each other without causing tectonic plates slip past each other.
    [Show full text]
  • Continuing Megathrust Earthquake Potential in Chile After the 2014 Iquique Earthquake
    LETTER doi:10.1038/nature13677 Continuing megathrust earthquake potential in Chile after the 2014 Iquique earthquake Gavin P. Hayes1, Matthew W. Herman2, William D. Barnhart1, Kevin P. Furlong2,Seba´stian Riquelme3, Harley M. Benz1, Eric Bergman4, Sergio Barrientos3, Paul S. Earle1 & Sergey Samsonov5 The seismic gap theory1 identifies regions of elevated hazard based a seismic hazard perspective is that the fault can host another event of on a lack of recent seismicity in comparison with other portions of a a similar magnitude. Although a great-sized earthquake here had been fault.It has successfully explained past earthquakes(see, for example, expected, it is possible that this event was not it10. ref. 2) and is useful for qualitatively describing where large earth- Sections of this subduction zone have ruptured since 1877 (Fig. 1), quakes might occur. A large earthquake had been expected in the most notably in 1967, in a M 7.4 event between ,21.5u Sand22u S, and subduction zone adjacent to northern Chile3–6, which had not rup- inthe 2007 M 7.7 Tocopillaearthquake between ,22u Sand23.5u S.Slip tured in a megathrust earthquake since a M 8.8 event in 1877. On during these events was limited to the deeper extent of the seismogenic 1 April 2014 a M 8.2 earthquake occurred within this seismic gap. zone, leaving shallower regions unruptured6,11. Farther south, the 1995 Here we present an assessment of the seismotectonics of the March– M 8.1 Antofagasta earthquake broke the seismogenic zone immediately April 2014 Iquique sequence, including analyses of earthquake reloca- south of the Mejillones Peninsula, a feature argued to be a persistent bar- tions, moment tensors, finite fault models, moment deficit calculations rier to rupture propagation11,12.
    [Show full text]
  • Stress, Rigidity and Sediment Strength Control Megathrust Earthquake and Tsunami Dynamics
    Stress, rigidity and sediment strength control megathrust earthquake and tsunami dynamics Thomas Ulrich,1∗ Alice-Agnes Gabriel,1 Elizabeth H. Madden2 1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitat¨ Munchen,¨ Munich, Germany 2 Observatorio´ Sismologico,´ Instituto de Geociencias,ˆ Universidade de Bras´ılia, Bras´ılia, Brazil ∗E-mail: [email protected] July 31, 2020 Megathrust faults host the largest earthquakes on Earth which can trigger cascading hazards such as devastating tsunamis. Determining characteristics that control subduction zone earth- quake and tsunami dynamics is critical to mitigate megathrust hazards, but is impeded by struc- tural complexity, large spatio-temporal scales, and scarce or asymmetric instrumental cover- age. Here we show that tsunamigenesis and earthquake dynamics are controlled by along-arc variability in regional tectonic stresses together with depth-dependent variations in rigidity and yield strength of near-fault sediments. We aim to identify dominant regional factors controlling megathrust hazards. To this end, we demonstrate how to unify and verify the required initial conditions for geometrically complex, multi-physics earthquake-tsunami modeling from inter- disciplinary geophysical observations. We present large-scale computational models of the 2004 Sumatra-Andaman earthquake and Indian Ocean tsunami that reconcile near- and far-field seis- mic, geodetic, geological, and tsunami observations and reveal tsunamigenic trade-offs between slip to the trench, splay faulting, and bulk yielding of the accretionary wedge. Our computa- tional capabilities render possible the incorporation of present and emerging high-resolution 1 observations into dynamic-rupture-tsunami models. Our findings highlight the importance of regional-scale structural heterogeneity to decipher megathrust hazards.
    [Show full text]