DOCSLIB.ORG

Shape of the Subducted Rivera and Cocos Plates in Southern Mexico

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Shape of the Subducted Rivera and Cocos Plates in Southern Mexico JOURNALOF GEOPHYSICAL RESEARCH, VOL. 100, NO. B7, PAGES 12,357-12,373, JULY 10, 1995 Shapeof the subductedRivera and Cocosplates in southern Mexico: Seismic and tectonicimplications Mario Pardo and Germdo Sufirez Insfitutode Geoffsica,Universidad Nacional Aut6noma de M6xico Abstract.The geometry of thesubducted Rivera and Cocos plates beneath the North American platein southernMexico was determined based on the accurately located hypocenters oflocal and te!eseismicearthquakes. The hypocenters ofthe teleseisms were relocated, and the focal depths of 21 eventswere constrainedusing a bodywave inversion scheme. The suductionin southern Mexicomay be approximated asa subhorizontalslabbounded atthe edges by the steep subduction geometryof theCocos plate beneath the Caribbean plate to the east and of theRivera plate beneath NorthAmerica to thewest. The dip of theinterplate contact geometry is constantto a depthof 30 kin,and lateral changes in thedip of thesubducted plate are only observed once it isdecoupled fromthe overriding plate. On thebasis of theseismicity, the focal mechanisms, and the geometry ofthe downgoing slab, southern Mexico may be segmented into four regions ß(1) theJalisco regionto thewest, where the Rivera plate subducts at a steepangle that resembles the geometry of theCocos plate beneath the Caribbean plate in CentralAmerica; (2) theMichoacan region, where thedip angleof theCocos plate decreases gradually toward the southeast, (3) theGuerrero-Oaxac.a region,bounded approximately by theonshore projection of theOrozco and O'Gorman fracture zones,where the subducted slab is almostsubhorizontal and underplates the upper continental plate for about250 kin, and (4) the southernOaxaca and Chiapas region, in southeasternMexico, wherethe dip of the subductiongradually increases to a steepersubduction in CentralAmerica. Thesedrastic changes in dip do not appearto takeplace on tearfaults, suggesting that smooth contortionsaccommodate these changes in geometry.The inferred80 and 100 km depthcontours of the subducted slab lie beneath the southernfront of the Trans-Mexican Volcanic Belt, suggestingit is directlyrelated to the subduction.Thus the observed nonparallelism with the MiddleAmerican Trench is apparentlydue to thechanging geometry of theRivera and Cocos platesbeneath the North American plate in southernMexico, and not to zones of weakness in the crustof the North Americanplate as someauthors have suggested. Introduction takes place on a fold. They also suggestedthat to the southeast,the changein dip may be related to differencesin The seismicity and tectonics of southern Mexico are the age of oceanic lithosphere on either side of the characterizedby the subductionof the oceanicCocos and Tehuantepecridge. Riveraplates beneath the North Americanlithosphere along Until recently, the acceptedview was that the Cocos plate the Middle American Trench. Several studies have shown that subductsbeneath central Mexico at a constantand relatively this subductionzone exhibits lateral variations in the dip of shallowangle of ~12 to 15ø [Stoiberand Carr, 1973;Hanus the subductedoceanic lithosphere[e.g., Molnar and Sykes, and Vanek, 1978; Havskov et al., 1982; Burbach et al., 19.84; 1969; Stoiber and Carr, 1973; Dean and Drake, 1978; Nixon, Bevis and lsacks, !984; Singh and Mortera, 1991]. Using 1982; Beyis and lsacks, 1984; Burbach et aL, 1984; Ponce et data from a permanentlocal network, Sutirez et al. [1990] al., 1992]. A steep subductiongeometry in southeastern definedthe geometryof the subductedplate in more detail and Mexico [Ponce et al., 1992] and in the Jaliscoregion of showed that in central Mexico the slab does not subduct at a westernMexico [Pardoand Sudrez,1993] bound a slabdipping steadyshallow angle. Instead,after an initial dip of-15 ø, the apparentlyat a very shallowangle in centralMexico. slab becomesalmost subhorizontal and underplatesthe North On the basis of teleseismic data, Burbach et aI. [19134] American upper lithosphere. This plate geometry is concludedthat the subductedCocos plate can be dividedinto reminiscent of that found in central Peru and central Chile, thesethree major regions dipping at differentangles. Beyis where the Nazca plate also subductshorizontally beneath the andlsacks [1984], using a hypocentraltrend surface analysis, SouthAmerican upper lithosphere. findno evidenceof tearfaulting separating these segments of Perhapsone of the more striking tectonic features in thesubducted lithosphere •[nd" suggested that the transition southern Mexico is the location of the Trans-Mexican Volcanic Belt. The Trans-Mexican Volcanic Belt crosses southern Mexico from east to west at about I9øN. The distributionof the volcanicarc is oblique(-16 ø) relativeto the 1Nowat Departamento deGeoffsica, Universidad deChile, Santiago. Middle American Trench (Figure 1), in an unusal geometry which is not parallel to the subductionzone. The Trans- Copyright1995 by theAmerican Geophysical Union. MexicanVolcanic Belt is ~100 km wide andis cut by a Paperhumber 95JB00919. sequenceof grabensthat are obliquerelative to the general 0148-0227/95/95JB.,00919505.00 trend of the arc [Nixon, 1982]. ' 12,357 12,358 PARDO AND SUAREZ: SUBDUCTION OF THE RIVERA AND COCOS PLATES -115" - 110 ø - 105" - 1 O0 ø -95 ø -90 ø -85 ø -80 ø 25 25 ø NORTH AMERICA CARIBE 20" 20 ø PACIFIC 15' 15" -'OCOS.' 10' 10 ø -115' -110 ø -105 ø -100 ø -95 ø -90 ø -85 ø -80 ø Figure 1. General tectonic setting of the study area. Five lithosphericplates arc shown: Pacific, Rivera, Coco.,,, North A•nerica, and Caribbean. Relative convergence rates (cm/yr) between the {•ceanic and continental plates are indicated by open arrows, and absolute motions of the upper plates relative to a hot spot rra•ne of reference ,ire shown by shaded arrows. The abrcviations are EPR, East Pacific Rise; TFZ, Tamayo Fracture Zone; RFZ, Rivera FractureZone; OFZ, Orozco Fracture Zone; OGFZ, O'Gorman Fracture Zone; TR, TchuantcpecRidge; MAT, Middle AmericanTrench; JB, JaliscoBlock; CG, Colima Graben;EG, E1 Gordo Graben. Solid triangles indicate Quaternaryvolcanism, and the crossedarea indicates the Trans- Mexican Volcanic Belt (TMVB). The volcanic arc erupted since the Miocene and mostly Volcanic Belt is presentedhere. The availability o1'data from during the Plioccne and Quaternary. A diversity of structures permanentand temporary local networksand the occurrenceof such as large strato-volcanoes, monogenetic cineritic cones, recentearthquakes recorded at tcleseismicdistances which had shield volcanoes, and several calderas are found on the not been studied previously otter tin excellent opportunityto volcanic belt. The chemical and petrologicai characteristics understand this region ol' complex subduction geometry in .of the Trans-Mexican Volcanic Belt indicate that, in general, greater detail. the volcanic sequences that form this belt are c,lic-alkaline, The purposeof this study is to determinethe geometryof although some localized zones of alealine volcanism exist the subducted Cocos and Rivera plate, based on all the along the Trans-Mexican Volcanic Belt, especially in western available and reliable hypocenter locations of earthquakes Mexico [e.g., Luhr et al., 1985; Allan et al., 1991]. The recorded with local and teleseismic networks, and to studythe radiometric dating of volcanic rocks and the broad nature of regional distribution of stresseswith reported and newly the Trans-Mexican Volcanic Belt suggest the migration of determined focal mechanisms. Together, these data are volcanism toward the trench sihce 5.3 Ma [Delgado et al., analyzedto determinean integralmodel of the subductionin 1993]. southernMexico and its implicationson the seismicityand A number of contrasting hypotheseshave been proposedto tectonics of' the area. account for the nonparallelism of the Trans-Mexican Volcanic Belt relative to the Middle American Trench and its relation to Tectonic Setting the subductedoceanic plate. These hypothesescan be divided This studyincludes the subductionof the Rivera andCocos into two groups: (1) those which favor a direct association plates in southernMexico, west of the intersectionof the between subduction and volcanism [e.g., Molnar and Sykes, 1969; Demant and Robin, 1975; Nixon, 1982; Burbach et al., Tehuantepecridge with the Middle American Trench (Figure 1). Accordingto Mammerickxand Klitgord [1982], the tectonic 1984; Suc•rezand Singh, 1986], and (2) those which suggest that the Trans-Mexican Volcanic Belt bears no direct tectonic historyof this regionfor the last 25 m.y. hassuffered at least three major plate reorganizations.The old Farallonplate relation with the subduction along the Middle American evolved first to the Guadalupe plate, which was later Trench and explain its origin as resulting from zones of weakness within the crust of southern M6xico, inherited from segmentedinto the actual Rivera and Cocosplates. The positionof thespreading centers moved east, from about 12.5 earlier episodes of deformation [e.g., Mooser, 1972; Gastil to 11 Ma, to the Mathematician seamounts. Later, between and Jensky, 1973; Shurbet and Cebull, 1973; Johnson and 6.3 to 3.5 Ma, it shifted to its actual position of the East Harrison, 1989]. Pacific Rise (EPR). An integral study that takes into account the geometry of the subducted Rivera and Cocos plates beneath the North Rivera Plate American lithosphere (NW of 94øW), the stressdistribution in the subducted slab, and the relation between the subduction Theexistence of thesmall Rivera plate was first suggested process and the anomalous
Load more

Recommended publications
  • Cambridge University Press 978-1-108-44568-9 — Active Faults of the World Robert Yeats Index More Information
    Cambridge University Press 978-1-108-44568-9 — Active Faults of the World Robert Yeats Index More Information Index Abancay Deflection, 201, 204–206, 223 Allmendinger, R. W., 206 Abant, Turkey, earthquake of 1957 Ms 7.0, 286 allochthonous terranes, 26 Abdrakhmatov, K. Y., 381, 383 Alpine fault, New Zealand, 482, 486, 489–490, 493 Abercrombie, R. E., 461, 464 Alps, 245, 249 Abers, G. A., 475–477 Alquist-Priolo Act, California, 75 Abidin, H. Z., 464 Altay Range, 384–387 Abiz, Iran, fault, 318 Alteriis, G., 251 Acambay graben, Mexico, 182 Altiplano Plateau, 190, 191, 200, 204, 205, 222 Acambay, Mexico, earthquake of 1912 Ms 6.7, 181 Altunel, E., 305, 322 Accra, Ghana, earthquake of 1939 M 6.4, 235 Altyn Tagh fault, 336, 355, 358, 360, 362, 364–366, accreted terrane, 3 378 Acocella, V., 234 Alvarado, P., 210, 214 active fault front, 408 Álvarez-Marrón, J. M., 219 Adamek, S., 170 Amaziahu, Dead Sea, fault, 297 Adams, J., 52, 66, 71–73, 87, 494 Ambraseys, N. N., 226, 229–231, 234, 259, 264, 275, Adria, 249, 250 277, 286, 288–290, 292, 296, 300, 301, 311, 321, Afar Triangle and triple junction, 226, 227, 231–233, 328, 334, 339, 341, 352, 353 237 Ammon, C. J., 464 Afghan (Helmand) block, 318 Amuri, New Zealand, earthquake of 1888 Mw 7–7.3, 486 Agadir, Morocco, earthquake of 1960 Ms 5.9, 243 Amurian Plate, 389, 399 Age of Enlightenment, 239 Anatolia Plate, 263, 268, 292, 293 Agua Blanca fault, Baja California, 107 Ancash, Peru, earthquake of 1946 M 6.3 to 6.9, 201 Aguilera, J., vii, 79, 138, 189 Ancón fault, Venezuela, 166 Airy, G.
    [Show full text]
  • Kinematic Reconstruction of the Caribbean Region Since the Early Jurassic
    Earth-Science Reviews 138 (2014) 102–136 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Kinematic reconstruction of the Caribbean region since the Early Jurassic Lydian M. Boschman a,⁎, Douwe J.J. van Hinsbergen a, Trond H. Torsvik b,c,d, Wim Spakman a,b, James L. Pindell e,f a Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands b Center for Earth Evolution and Dynamics (CEED), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway c Center for Geodynamics, Geological Survey of Norway (NGU), Leiv Eirikssons vei 39, 7491 Trondheim, Norway d School of Geosciences, University of the Witwatersrand, WITS 2050 Johannesburg, South Africa e Tectonic Analysis Ltd., Chestnut House, Duncton, West Sussex, GU28 OLH, England, UK f School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, UK article info abstract Article history: The Caribbean oceanic crust was formed west of the North and South American continents, probably from Late Received 4 December 2013 Jurassic through Early Cretaceous time. Its subsequent evolution has resulted from a complex tectonic history Accepted 9 August 2014 governed by the interplay of the North American, South American and (Paleo-)Pacific plates. During its entire Available online 23 August 2014 tectonic evolution, the Caribbean plate was largely surrounded by subduction and transform boundaries, and the oceanic crust has been overlain by the Caribbean Large Igneous Province (CLIP) since ~90 Ma. The consequent Keywords: absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into GPlates Apparent Polar Wander Path the global circuit of plate motions.
    [Show full text]
  • SUMMARIES of TECHNICAL REPORTS, VOLUME X Prepared by Participants in NATIONAL EARTHQUAKE HAZARDS REDUCTION PROGRAM June 1980
    UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Office of Earthquake Studies SUMMARIES OF TECHNICAL REPORTS, VOLUME X Prepared by participants in NATIONAL EARTHQUAKE HAZARDS REDUCTION PROGRAM June 1980 OPEN-FILE REPORT 80-842 This report is preliminary and has not been edited or reviewed for conformity with Geological Survey standards and nomenclature Menlo Park, California 1980 CONTENTS Earthquake Hazards Reduction Program I. Earthquake Hazards Studies (H) Page Objective 1, Establish an accurate and reliable national earthquake data base.——————————————————• Objective 2. Delineate and evaluate earthquake hazards and risk in the United States on a national scale. ——————————————————————————• 66 Objective 3. Delineate and evaluate earthquake hazards and risk in earthquake-prone urbanized regions in the western United States.——————————————• 77 Objective 4, Delineate and evaluate earthquake hazards and risk in earthquake-prone regions in the eastern United States. ————— —————————— — ———— 139 Objective 5. Improve capability to evaluate earthquake potential and predict character of surface faulting.———————————————— ————————— 171 Objective 6. Improve capability to predict character of damaging ground shaking.———————————————— 245 Objective 7. Improve capability to predict incidence, nature and extent of earthquake-induced ground failures, particularly landsliding and liquefaction.--——— 293 Objective 8. Improve capability to predict earthquake losses.— 310 II. Earthquake Prediction Studies (P) Objective 1. Observe at a reconnaissance
    [Show full text]
  • Morphotectonic Zones Along the Coast of the Pacific Continental Margin, Southern Mexico
    See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/223022792 Morphotectonic zones along the coast of the Pacific continental margin, southern Mexico Article in Geomorphology · July 1999 DOI: 10.1016/S0169-555X(99)00016-1 CITATIONS READS 37 76 2 authors, including: J. Urrutia Fucugauchi Universidad Nacional Autónoma de México 542 PUBLICATIONS 18,205 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: CHICAGO View project Arco magmático Pérmico relacionado con la zona de sutura Ouachita en Chihuahua, México View project All content following this page was uploaded by J. Urrutia Fucugauchi on 31 January 2014. The user has requested enhancement of the downloaded file. Geomorphology 28 Ž1999. 237–250 Morphotectonic zones along the coast of the Pacific continental margin, southern Mexico Marıa-Teresa´ Ramırez-Herrera´ a,), Jaime Urrutia-Fucugauchi b,1 a Instituto de Geografıa,´ Departamento de Geografıa´ Fısica,´ UNAM, Ciudad UniÕersitaria, C.P. 04510, Mexico, D.F., Mexico b Instituto de Geofısica,´ Laboratorio de Paleomagnetismo y Geofısica´ Nuclear, UNAM, Ciudad UniÕersitaria, C.P. 04510 Mexico, D.F., Mexico Received 15 December 1997; received in revised form 20 August 1998; accepted 22 November 1998 Abstract Geomorphic analysis, employing topographic, morphologic, geologic, and bathymetric maps, and field studies show that the morphology of the southern coast of Mexico can be linked to lateral variations in the geometry and tectonism of the subduction zone. A reconnaissance study, based on the regional morphological characteristics and correlation with seismotectonic segments, regional tectonics and major bathymetric features, allows identification of several morphotectonic zones along the coast of southern Mexico: Ž1.
    [Show full text]
  • Plate Tectonics Review from Valerie Nulisch Some Questions (C) 2017 by TEKS Resource System
    Plate Tectonics Review from Valerie Nulisch Some questions (c) 2017 by TEKS Resource System. Some questions (c) 2017 by Region 10 Educational Service Center. Some questions (c) 2017 by Progress Testing. Page 2 GO ON A student wanted to make a model of the Earth. The student decided to cut a giant Styrofoam ball in half and paint the layers on it to show their thickness. 1 Which model below best represents the layers of the Earth? A B C D Page 3 GO ON 2 A student is building a model of the layers of the Earth. Which material would best represent the crust? F Grouping of magnetic balls G Styrofoam packing pellets H Bag of shredded paper J Thin layer of graham crackers 3 Your teacher has asked you to make a model of the interior of the Earth. In your model, how do the thicknesses of the lithosphere and crust compare? A The lithosphere is thinner than the crust. B The lithosphere is exactly the same thickness as the crust. C The lithosphere is thicker than the crust. D The lithosphere is thicker than the oceanic crust, but thinner than the continental crust. 4 Sequence the layers of the Earth in order from the exterior surface to the interior center. F Lithosphere, mantle, inner core, outer core, crust, asthenosphere G Inner core, outer core, mantle, asthenosphere, lithosphere, crust H Crust, mantle, outer core, inner core, asthenosphere, lithosphere J Crust, lithosphere, asthenosphere, mantle, outer core, inner core Page 4 GO ON 5 The tectonic plate labeled A in the diagram is the A Eurasian Plate B Indo-Australian Plate C Pacific Plate D African Plate Page 5 GO ON 6 The tectonic plate labeled B in the diagram is the — F Eurasian Plate G Indo-Australian Plate H Pacific Plate J North American Plate Page 6 GO ON Directions: The map below shows Earth's tectonic plates; six of them are numbered.
    [Show full text]
  • Interplate Coupling Along the Nazca Subduction Zone on the Pacific Coast of Colombia Deduced from Geored GPS Observation Data
    Volume 4 Quaternary Chapter 15 Neogene https://doi.org/10.32685/pub.esp.38.2019.15 Interplate Coupling along the Nazca Subduction Published online 28 May 2020 Zone on the Pacific Coast of Colombia Deduced from GeoRED GPS Observation Data Paleogene Takeshi SAGIYA1 and Héctor MORA–PÁEZ2* 1 [email protected] Nagoya University Disaster Mitigation Research Center Nagoya, Japan Abstract The Nazca Plate subducts beneath Colombia and Ecuador along the Pacific Cretaceous coast where large megathrust events repeatedly occur. Distribution of interplate 2 [email protected] Servicio Geológico Colombiano coupling on the subducting plate interface based on precise geodetic data is im- Dirección de Geoamenazas portant to evaluate future seismic potential of the megathrust. We analyze recent Space Geodesy Research Group Diagonal 53 n.° 34–53 continuous GPS data in Colombia and Ecuador to estimate interplate coupling in the Bogotá, Colombia Jurassic Nazca subduction zone. To calculate the interplate coupling ratio, in addition to the * Corresponding author MORVEL plate velocities, three different Euler poles for the North Andean Block are tested but just two of them yielded similar results and are considered appropriate for discussing the Pacific coastal area. The estimated coupling distribution shows four main locked patches. The middle two locked patches correspond to recent large Triassic earthquakes in this area in 1942, 1958, and 2016. The southernmost locked patch may be related to slow slip events. The northern locked patch has a smaller coupling ra- tio of less than 0.5, which may be related to the large earthquake in 1979. However, because of the sparsity of the GPS network, detailed interpretation is not possible.
    [Show full text]
  • Back-Arc Opening and the Mode of Subduction
    VOL.84, NO. B3 JOURNALOF GEOPHYSICALRESEARCH MARCH10, 1979 Back-ArcOpening and the Mode of Subduction SEIYA UYEDA EarthquakeResearch Institute, University of Tokyo,Tokyo, Japan HIROO K ANAMORI SeismologicalLaboratory, California Institute of Technology,Pasadena, California 91125 Trench-arcsystems (subduction zones) can be classified into two types depending onwhether or not activelyopening back-arc basins are associated with them. This suggests that subduction of an oceanic plateis not a sufficientcondition for back-arc opening, though it may be necessary one. Mechanisms that causethe distinction between the two types have been investigated. Earthquake studies suggest that there isa significantdifference inthe mode of plate motion at interplate boundaries between the two types of trench-arcsystems. Extreme cases are Chile, where plate motion is seismic, and the M arianas arc, where it is aseismic.This difference seems to indicatethat the stress state in theback-arc area differs between the twotypes: compression in the Chilean type and tension in theMarianas type. This difference in thestress stateis alsomanifested in other tectonic features, such as topography, gravity, volcanic activity, and crustalmovement. Two possible mechanisms forthe difference between the two types are suggested: (1) Thenature of thecontact zone between upper and lower plates chahges from tight coupling (Chile) to decoupling(the Marianas) through the evolutionary process ofsubduction. The decoupling results inan oceanwardretreat of the trench and back-arc opening. (2) The downgoing slab is anchored tothe mantle, sothat the position of a trenchis also fixed with respect to themantle. Since the motion in themantle is slowcompared tothat of surface plates, it is the motion of the landward plate which controls the opening and nonopeningof back-arcs.
    [Show full text]
  • 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.
    [Show full text]
  • Measurements of Upper Mantle Shear Wave Anisotropy from a Permanent Network in Southern Mexico
    GEOFÍSICA INTERNACIONAL (2013) 52-4: 385-402 ORIGINAL PAPER Measurements of upper mantle shear wave anisotropy from a permanent network in southern Mexico Steven A. C. van Benthem, Raúl W. Valenzuela* and Gustavo J. Ponce Received: November 13, 2012; accepted: December 14, 2012; published on line: September 30, 2013 Resumen Abstract Se midió la anisotropía para las ondas de cortante 8SSHU PDQWOH VKHDU ZDYH DQLVRWURS\ XQGHU en el manto superior por debajo de estaciones VWDWLRQVLQVRXWKHUQ0H[LFRZDVPHDVXUHGXVLQJ en el sur de México usando fases SKS. Las records of SKS phases. Fast polarization directions direcciones de polarización rápida donde la placa ZKHUHWKH&RFRVSODWHVXEGXFWVVXEKRUL]RQWDOO\ de Cocos se subduce subhorizontalmente están are oriented in the direction of the relative orientadas aproximadamente paralelas con el PRWLRQEHWZHHQWKH&RFRVDQG1RUWK$PHULFDQ movimiento relativo entre las placas de Cocos y plates, and are trench-perpendicular. This América del Norte y además son perpendiculares SDWWHUQLVLQWHUSUHWHGDVVXEVODEHQWUDLQHGÀRZ DODWULQFKHUD3RUORWDQWRVHLQ¿HUHTXHODSODFD and is similar to that observed at the Cascadia VXEGXFLGD DUUDVWUD HO PDQWR TXH VH HQFXHQWUD subduction zone. Earlier studies have pointed SRUGHEDMR\ORKDFHÀXLU HQWUDLQHGÀRZ 8QD out that both regions have in common the young situación similar existe en la zona de subducción age of the subducting lithosphere. Changes in the GH&DVFDGLD(VWXGLRVSUHYLRVKDQVHxDODGRTXH RULHQWDWLRQRIWKHIDVWD[HVDUHREVHUYHGZKHUH estas dos regiones tienen en común la subducción the subducting
    [Show full text]
  • Geometry and Seismic Properties of the Subducting Cocos Plate in Central Mexico Y
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, B06310, doi:10.1029/2009JB006942, 2010 Click Here for Full Article Geometry and seismic properties of the subducting Cocos plate in central Mexico Y. Kim,1 R. W. Clayton,1 and J. M. Jackson1 Received 31 August 2009; revised 22 December 2009; accepted 25 January 2010; published 17 June 2010. [1] The geometry and properties of the interface of the Cocos plate beneath central Mexico are determined from the receiver functions (RFs) utilizing data from the Meso America Subduction Experiment (MASE). The RF image shows that the subducting oceanic crust is shallowly dipping to the north at 15° for 80 km from Acapulco and then horizontally underplates the continental crust for approximately 200 km to the Trans‐ Mexican Volcanic Belt (TMVB). The crustal image also shows that there is no continental root associated with the TMVB. The migrated image of the RFs shows that the slab is steeply dipping into the mantle at about 75° beneath the TMVB. Both the continental and oceanic Moho are clearly seen in both images, and modeling of the RF conversion amplitudes and timings of the underplated features reveals a thin low‐velocity zone between the plate and the continental crust that appears to absorb nearly all of the strain between the upper plate and the slab. By inverting RF amplitudes of the converted phases and their time separations, we produce detailed maps of the seismic properties of the upper and lower oceanic crust of the subducting Cocos plate and its thickness. High Poisson’s and Vp/Vs ratios due to anomalously low S wave velocity at the upper oceanic crust in the flat slab region may indicate the presence of water and hydrous minerals or high pore pressure.
    [Show full text]
  • Tectonic Segmentation of the North Andean Margin: Impact of the Carnegie Ridge Collision
    ELSEVIER Earth and Planetary Science Letters 168 (1999) 255±270 Tectonic segmentation of the North Andean margin: impact of the Carnegie Ridge collision M.-A. Gutscher a,Ł, J. Malavieille a, S. Lallemand a, J.-Y. Collot b a Laboratoire de GeÂophysique et Tectonique, UMR 5573, Universite Montpellier II, Place E. Bataillon, F-34095 Montpellier, Cedex 5, France b IRD, Geosciences Azur, Villefranche-sur-Mer, France Received 17 July 1998; accepted 2 March 1999 Abstract The North Andean convergent margin is a region of intense crustal deformation, with six great subduction earthquakes Mw ½ 7:8 this century. The regional pattern of seismicity and volcanism shows a high degree of segmentation along strike of the Andes. Segments of steep slab subduction alternate with aseismic regions and segments of ¯at slab subduction. This segmentation is related to heterogeneity on the subducting Nazca Plate. In particular, the in¯uence of the Carnegie Ridge collision is investigated. Four distinct seismotectonic regions can be distinguished: Region 1 ± from 6ëN to 2.5ëN with steep ESE-dipping subduction and a narrow volcanic arc; Region 2 ± from 2.5ëN to 1ëS showing an intermediate-depth seismic gap and a broad volcanic arc; Region 3 ± from 1ëS to 2ëS with steep NE-dipping subduction, and a narrow volcanic arc; Region 4 ± south of 2ëS with ¯at subduction and no modern volcanic arc. The Carnegie Ridge has been colliding with the margin since at least 2 Ma based on examination of the basement uplift signal along trench-parallel transects. The subducted prolongation of Carnegie Ridge may extend up to 500 km from the trench as suggested by the seismic gap and the perturbed, broad volcanic arc.
    [Show full text]
  • Plate Tectonics Passport
    What is plate tectonics? The Earth is made up of four layers: inner core, outer core, mantle and crust (the outermost layer where we are!). The Earth’s crust is made up of oceanic crust and continental crust. The crust and uppermost part of the mantle are broken up into pieces called plates, which slowly move around on top of the rest of the mantle. The meeting points between the plates are called plate boundaries and there are three main types: Divergent boundaries (constructive) are where plates are moving away from each other. New crust is created between the two plates. Convergent boundaries (destructive) are where plates are moving towards each other. Old crust is either dragged down into the mantle at a subduction zone or pushed upwards to form mountain ranges. Transform boundaries (conservative) are where are plates are moving past each other. Can you find an example of each type of tectonic plate boundary on the map? Divergent boundary: Convergent boundary: Transform boundary: What do you notice about the location of most of the Earth’s volcanoes? P.1 Iceland Iceland lies on the Mid Atlantic Ridge, a divergent plate boundary where the North American Plate and the Eurasian Plate are moving away from each other. As the plates pull apart, molten rock or magma rises up and erupts as lava creating new ocean crust. Volcanic activity formed the island about 16 million years ago and volcanoes continue to form, erupt and shape Iceland’s landscape today. The island is covered with more than 100 volcanoes - some are extinct, but about 30 are currently active.
    [Show full text]