TY - THES A1 - Lange, Dietrich T1 - The South Chilean subduction zone between 41° and 43.5°S : seismicity, structure and state of stress T1 - Die süd-chilenische Subduktionszone zwischen 41° und 43.5°S : Seismizität, Struktur und Spannungszustand N2 - Die stärksten Erdbeben treten an Subduktionszonen auf, so z.B. das stärkste instrumentell jemals gemessene Erdbeben vom 22. Mai 1960 mit einer Magnitude von 9,5 Mw in Süd Chile. In dieser Arbeit werden lokal gewonnene seismologische Daten aus dem zentralen Bereich des 1960er-Bebens vorgestellt. Das seismologische Netzwerk umfasste den chilenischen Forearc zwischen Tiefseegraben und den vulkanischen Bogen zwischen 41,5°-43,5°S und überdeckte sowohl die Insel Chiloé als auch die Nord-Süd-streichende Liquiñe-Ofqui Störungszone (LOFZ). Zwischen November 2004 und Oktober 2005 konnten 364 lokale Ereignisse registriert werden. Die gewonnen Aufzeichnungen erlauben Aussagen sowohl über das aktuelle Spannungsfeld im Forearc als auch über das lokale Geschwindigkeitsmodell und die Geometrie der subduzierten Benioff-Zone. Mit einer Auswahl von P- und S-Laufzeiten von gut lokalisierbaren Erdbeben wurden ein Minimum 1-D Geschwindigkeitsmodell, Stationsresiduen und die Hypozentralparameter invertiert. Dieses Geschwindigkeitsmodell diente als Startmodell für die 2-D Tomographie. Das 2-D vp-Modell zeigt eine Zone erhöhter Geschwindigkeiten unterhalb des Längstals und des östlichen Bereiches der Insel Chiloé, die als Mantelaufwölbung interpretiert werden kann. Die Benioff-Zone wird als eine mit ca. 30° ostwärts einfallende Struktur abgebildet. Die seismische Hauptaktivität findet parallel zur Küste der Insel Chiloé in Tiefen zwischen 12 und 30 km statt; es handelt sich um Beben, die wahrscheinlich auf der Plattengrenzfläche stattfinden. In Tiefen über 70 km lässt die Seismizität bereits stark nach, die tiefsten Beben wurden in 120 km Tiefe registriert. Die Abwesenheit tieferer Seismizität wird auf das junge Alter (und eine damit verbundene hohe Temperatur) der ozeanischen Platte zurückgeführt. Neben der Seismizität in der Benioff-Zone treten flache, krustale Beben in verschiedenen Häufungen entlang des magmatischen Bogens auf. Diese Bereiche erhöhter Seismizität sind räumlich mit der LOFZ und den Vulkanen Chaitén, Michinmahuida und Corcovado verknüpft. Beben bis zu einer Magnitude von 3,8 Mw zeigen die gegenwärtige Aktivität der LOFZ. Herdflächen entlang der LOFZ wurden aus Momententensor-Inversion anhand von Amplitudenspektren von Raumwellen gewonnen. Ergebnisse einer Spannungsfeldinversion zeigen ein Blattverschiebungsregime für den magmatischen Bogen und ein Überschiebungsregime für Beben in der Benioff-Zone auf. Die hier gemachten seismologischen Beobachtungen, zusammen mit teleseismischen Erdbeben und geologischen Befunden, unterstützen die Modellvorstellung eines sich nordwärts bewegenden kontinentalen Forearc-Blocks für Süd Chile. N2 - While the northern and central part of the South American subduction zone has been intensively studied, the southern part has attracted less attention, which may be due to its difficult accessibility and lower seismic activity. However, the southern part exhibits strong seismic and tsunamogenic potential with the prominent example of the Mw=9.5 May 22, 1960 Valdivia earthquake. In this study data from an amphibious seismic array (Project TIPTEQ) is presented. The network reached from the trench to the active magmatic arc incorporating the Island of Chiloé and the north-south trending Liquiñe-Ofqui fault zone (LOFZ). 364 local events were observed in an 11-month period from November 2004 until October 2005. The observed seismicity allows to constrain for the first time the current state of stress of the subducting plate and magmatic arc, as well as the local seismic velocity structure. The downgoing Benioff zone is readily identifiable as an eastward dipping plane with an inclination of ~30°. Main seismic activity occurred predominantly in a belt parallel to the coast of Chiloé Island in a depth range of 12-30 km, which is presumably related to the plate interface. The down-dip termination of abundant intermediate depth seismicity at approximately 70 km depth seems to be related to the young age (and high temperature) of the oceanic plate. A high-quality subset of events was inverted for a 2-D velocity model. The vp model resolves the sedimentary basins and the downgoing slab. Increased velocities below the longitudinal valley and the eastern part of Chiloé Island suggest the existence of a mantle bulge. Apart from the events in the Benioff Zone, shallow crustal events were observed mainly in different clusters along the magmatic arc. These crustal clusters of seismicity are related to the LOFZ, as well as to the volcanoes Chaitén, Michinmahuida and Corcovado. Seismic activity up to a magnitude of 3.8 Mw reveals the recent activity of the fault zone. Focal mechanisms for the events along the LOFZ were calculated using a moment tensor inversion of amplitude spectra for body waves which mostly yield strike-slip mechanisms indicating a SW-NE striking of sigma_1 for the LOFZ. Focal mechanism stress inversion indicates a strike-slip regime along the arc and a thrust regime in the Benioff zone. The observed deformation - which is also revealed by teleseismic observations - suggests a confirmation for the proposed northward movement of a forearc sliver acting as a detached continental micro-plate. KW - Süd Chile KW - Liquiñe-Ofqui Störungszone KW - lokale Seismitität KW - Momententensoren KW - Subduktionszone KW - subduction zone KW - local Seismicity KW - Liquiñe-Ofqui fault zone KW - South Chile KW - stress partitioning Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18948 ER - TY - JOUR A1 - Hetenyi, Gyorgy A1 - Molinari, Irene A1 - Clinton, John A1 - Bokelmann, Gotz A1 - Bondar, Istvan A1 - Crawford, Wayne C. A1 - Dessa, Jean-Xavier A1 - Doubre, Cecile A1 - Friederich, Wolfgang A1 - Fuchs, Florian A1 - Giardini, Domenico A1 - Graczer, Zoltan A1 - Handy, Mark R. A1 - Herak, Marijan A1 - Jia, Yan A1 - Kissling, Edi A1 - Kopp, Heidrun A1 - Korn, Michael A1 - Margheriti, Lucia A1 - Meier, Thomas A1 - Mucciarelli, Marco A1 - Paul, Anne A1 - Pesaresi, Damiano A1 - Piromallo, Claudia A1 - Plenefisch, Thomas A1 - Plomerova, Jaroslava A1 - Ritter, Joachim A1 - Rumpker, Georg A1 - Sipka, Vesna A1 - Spallarossa, Daniele A1 - Thomas, Christine A1 - Tilmann, Frederik A1 - Wassermann, Joachim A1 - Weber, Michael A1 - Weber, Zoltan A1 - Wesztergom, Viktor A1 - Zivcic, Mladen A1 - Abreu, Rafael A1 - Allegretti, Ivo A1 - Apoloner, Maria-Theresia A1 - Aubert, Coralie A1 - Besancon, Simon A1 - de Berc, Maxime Bes A1 - Brunel, Didier A1 - Capello, Marco A1 - Carman, Martina A1 - Cavaliere, Adriano A1 - Cheze, Jerome A1 - Chiarabba, Claudio A1 - Cougoulat, Glenn A1 - Cristiano, Luigia A1 - Czifra, Tibor A1 - Danesi, Stefania A1 - Daniel, Romuald A1 - Dannowski, Anke A1 - Dasovic, Iva A1 - Deschamps, Anne A1 - Egdorf, Sven A1 - Fiket, Tomislav A1 - Fischer, Kasper A1 - Funke, Sigward A1 - Govoni, Aladino A1 - Groschl, Gidera A1 - Heimers, Stefan A1 - Heit, Ben A1 - Herak, Davorka A1 - Huber, Johann A1 - Jaric, Dejan A1 - Jedlicka, Petr A1 - Jund, Helene A1 - Klingen, Stefan A1 - Klotz, Bernhard A1 - Kolinsky, Petr A1 - Kotek, Josef A1 - Kuhne, Lothar A1 - Kuk, Kreso A1 - Lange, Dietrich A1 - Loos, Jurgen A1 - Lovati, Sara A1 - Malengros, Deny A1 - Maron, Christophe A1 - Martin, Xavier A1 - Massa, Marco A1 - Mazzarini, Francesco A1 - Metral, Laurent A1 - Moretti, Milena A1 - Munzarova, Helena A1 - Nardi, Anna A1 - Pahor, Jurij A1 - Pequegnat, Catherine A1 - Petersen, Florian A1 - Piccinini, Davide A1 - Pondrelli, Silvia A1 - Prevolnik, Snjezan A1 - Racine, Roman A1 - Regnier, Marc A1 - Reiss, Miriam A1 - Salimbeni, Simone A1 - Santulin, Marco A1 - Scherer, Werner A1 - Schippkus, Sven A1 - Schulte-Kortnack, Detlef A1 - Solarino, Stefano A1 - Spieker, Kathrin A1 - Stipcevic, Josip A1 - Strollo, Angelo A1 - Sule, Balint A1 - Szanyi, Gyongyver A1 - Szucs, Eszter A1 - Thorwart, Martin A1 - Ueding, Stefan A1 - Vallocchia, Massimiliano A1 - Vecsey, Ludek A1 - Voigt, Rene A1 - Weidle, Christian A1 - Weyland, Gauthier A1 - Wiemer, Stefan A1 - Wolf, Felix A1 - Wolyniec, David A1 - Zieke, Thomas T1 - The AlpArray seismic network BT - a large-scale european experiment to image the alpine orogen JF - Surveys in Geophysics N2 - The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth. KW - Seismology KW - Alps KW - Seismic network KW - Geodynamics KW - Seismic imaging KW - Mountain building Y1 - 2018 U6 - https://doi.org/10.1007/s10712-018-9472-4 SN - 0169-3298 SN - 1573-0956 VL - 39 IS - 5 SP - 1009 EP - 1033 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Hannemann, Katrin A1 - Krüger, Frank A1 - Dahm, Torsten A1 - Lange, Dietrich T1 - Structure of the oceanic lithosphere and upper mantle north of the Gloria Fault in the eastern mid-Atlantic by receiver function analysis JF - Journal of geophysical research : Solid earth N2 - Receiver functions (RF) have been used for several decades to study structures beneath seismic stations. Although most available stations are deployed on shore, the number of ocean bottom station (OBS) experiments has increased in recent years. Almost all OBSs have to deal with higher noise levels and a limited deployment time (approximate to 1year), resulting in a small number of usable records of teleseismic earthquakes. Here we use OBSs deployed as midaperture array in the deep ocean (4.5-5.5km water depth) of the eastern mid-Atlantic. We use evaluation criteria for OBS data and beamforming to enhance the quality of the RFs. Although some stations show reverberations caused by sedimentary cover, we are able to identify the Moho signal, indicating a normal thickness (5-8km) of oceanic crust. Observations at single stations with thin sediments (300-400m) indicate that a probable sharp lithosphere-asthenosphere boundary (LAB) might exist at a depth of approximate to 70-80km which is in line with LAB depth estimates for similar lithospheric ages in the Pacific. The mantle discontinuities at approximate to 410km and approximate to 660km are clearly identifiable. Their delay times are in agreement with PREM. Overall the usage of beam-formed earthquake recordings for OBS RF analysis is an excellent way to increase the signal quality and the number of usable events. KW - receiver function KW - oceanic lithosphere and mantle KW - ocean bottom seismology Y1 - 2017 U6 - https://doi.org/10.1002/2016JB013582 SN - 2169-9313 SN - 2169-9356 VL - 122 SP - 7927 EP - 7950 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Collings, R. A1 - Lange, Dietrich A1 - Rietbrock, Andreas A1 - Tilmann, F. A1 - Natawidjaja, D. A1 - Suwargadi, B. A1 - Miller, M. A1 - Saul, Joschim T1 - Structure and seismogenic properties of the Mentawai segment of the Sumatra subduction zone revealed by local earthquake traveltime tomography JF - Journal of geophysical research : Solid earth N2 - On 12 September 2007, an M-w 8.4 earthquake occurred within the southern section of the Mentawai segment of the Sumatra subduction zone, where the subduction thrust had previously ruptured in 1833 and 1797. Traveltime data obtained from a temporary local seismic network, deployed between December 2007 and October 2008 to record the aftershocks of the 2007 event, was used to determine two-dimensional (2-D) and three-dimensional (3-D) velocity models of the Mentawai segment. The seismicity distribution reveals significant activity along the subduction interface and within two clusters in the overriding plate either side of the forearc basin. The downgoing slab is clearly distinguished by a dipping region of high Vp (8.0 km/s), which can be a traced to similar to 50 km depth, with an increased Vp/Vs ratio (1.75 to 1.90) beneath the islands and the western side of the forearc basin, suggesting hydrated oceanic crust. Above the slab, a shallow continental Moho of less than 30 km depth can be inferred, suggesting that the intersection of the continental mantle with the subducting slab is much shallower than the downdip limit of the seismogenic zone despite localized serpentinization being present at the toe of the mantle wedge. The outer arc islands are characterized by low Vp (4.5-5.8 km/s) and high Vp/Vs (greater than 2.0), suggesting that they consist of fluid saturated sediments. The very low rigidity of the outer forearc contributed to the slow rupture of the M-w 7.7 Mentawai tsunami earthquake on 25 October 2010. Y1 - 2012 U6 - https://doi.org/10.1029/2011JB008469 SN - 2169-9313 SN - 2169-9356 VL - 117 IS - 3 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Collings, R. A1 - Rietbrock, Andreas A1 - Lange, Dietrich A1 - Tilmann, F. A1 - Nippress, Stuart A1 - Natawidjaja, D. T1 - Seismic anisotropy in the sumatra subduction zone JF - Journal of geophysical research : Solid earth N2 - An important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting (SWS). In Sumatra, two temporary seismic networks were deployed between December 2007 and February 2009, covering the fore arc between the fore-arc islands to the back arc. We use SKS and local SWS measurements to determine the type, amount, and location of anisotropy. Local SWS measurements from the fore-arc islands exhibit trench-parallel fast directions which can be attributed to shape preferred orientation of cracks/fractures in the overriding sediments. In the Sumatran Fault region, the predominant fast direction is fault/trench parallel, while in the back-arc region it is trench perpendicular. The trench-perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge, while the fault-parallel measurements are similar to the fault-parallel fast directions observed for two crustal events at the Sumatran Fault. This suggests that there are two layers of anisotropy: one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the Sumatran Fault. SKS splitting results show a NNW-SSE fast direction with delay times of 0.8-3.0s. The fast directions are approximately parallel to the absolute plate motion of the subducting Indo-Australian Plate. The small delay times exhibited by the local SWS (0.05-0.45s), in combination with the large SKS delay times, suggest that the anisotropy generating the teleseismic SWS is dominated by entrained flow in the asthenosphere below the slab. KW - Sumatra KW - Anisotropy KW - Shear wave splitting KW - Subduction zone KW - Mantle rheology Y1 - 2013 U6 - https://doi.org/10.1002/jgrb.50157 SN - 2169-9313 SN - 2169-9356 VL - 118 IS - 10 SP - 5372 EP - 5390 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Hannemann, Katrin A1 - Krüger, Frank A1 - Dahm, Torsten A1 - Lange, Dietrich T1 - Oceanic lithospheric S-wave velocities from the analysis of P-wave polarization at the ocean floor JF - Geophysical journal international N2 - Our knowledge of the absolute S-wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S-wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P-wave polarization (apparent P-wave incidence angle) of teleseismic events to investigate the S-wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P-wave incidence angle at the ocean bottom dependent on the half-space S-wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBSs) to derive apparent S-wave velocity profiles. These profiles are dependent on the S-wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P-wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S-wave-velocity-depth models by a three-step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S-wave velocities. The apparent S-wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 and 0.9 km with S-wave velocities between 0.7 and 1.4 km s(-1). The estimated total crustal thickness varies between 4 and 10 km with S-wave velocities between 3.5 and 4.3 km s(-1). We find a slight increase of the total crustal thickness from similar to 5 to similar to 8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S-wave velocities decrease from values around 5.5 to 4.5 km s(-1) towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S-wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P-wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S-wave velocities for real and synthetic data to estimate S-wave velocity-depth models. KW - Time-series analysis KW - Body waves KW - Theoretical seismology KW - Oceanic transform and fracture zone processes Y1 - 2016 U6 - https://doi.org/10.1093/gji/ggw342 SN - 0956-540X SN - 1365-246X VL - 207 SP - 1796 EP - 1817 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Pesicek, J. D. A1 - Engdahl, E. R. A1 - Thurber, C. H. A1 - DeShon, H. R. A1 - Lange, Dietrich T1 - Mantle subducting slab structure in the region of the 2010 M8.8 Maule earthquake (30-40 degrees S), Chile JF - Geophysical journal international N2 - We present a new tomographic model of the mantle in the area of the 2010 M8.8 Maule earthquake and surrounding regions. Increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle, from the region of flat slab subduction north of the Maule rupture to the area of overlapping rupture between the 1960 M9.5 and the 2010 M8.8 events to the south. We have combined teleseismic primary and depth phase arrivals with available local arrivals to better constrain the teleseismic earthquake locations in the region, which we use to conduct nested regionalglobal tomography. The new model reveals the detailed structure of the flat slab and its transition to a more moderately dipping slab in the Maule region. South of the Maule region, a steeply dipping relic slab is imaged from similar to 200 to 1000 km depth that is distinct from the moderately dipping slab above it and from the more northerly slab at similar depths. We interpret the images as revealing both horizontal and vertical tearing of the slab at similar to 38 degrees S to explain the imaged pattern of slab anomalies in the southern portion of the model. In contrast, the transition from a horizontal to moderately subducting slab in the northern portion of the model is imaged as a continuous slab bend. We speculate that the tearing was most likely facilitated by a fracture zone in the downgoing plate or alternatively by a continental scale terrane boundary in the overriding plate. KW - Seismicity and tectonics KW - Seismic tomography KW - Subduction zone processes Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-246X.2012.05624.x SN - 0956-540X VL - 191 IS - 1 SP - 317 EP - 324 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Haberland, Christian A1 - Rietbrock, Andreas A1 - Lange, Dietrich A1 - Bataille, Klaus A1 - Hofmann, S. T1 - Interaction between forearc and oceanic plate at the south-central Chilean margin as seen in local seismic data JF - Geophysical research letters N2 - We installed a dense, amphibious, temporary seismological network to study the seismicity and structure of the seismogenic zone in southern Chile between 37° and 39°S, the nucleation area of the great 1960 Chile earthquake. 213 local earthquakes with 14.754 onset times were used for a simultaneous inversion for the 1‐D velocity model and precise earthquake locations. Relocated artificial shots suggest an accuracy of the earthquake hypocenter of about 1 km (horizontally) and 500 m (vertically). Crustal events along trench‐parallel and transverse, deep‐reaching faults reflect the interseismic transpressional deformation of the forearc crust due to the subduction of the Nazca plate. The transverse faults seems to accomplish differential lateral stresses between subduction zone segments. Many events situated in an internally structured, planar seismicity patch at 20 to 40 km depth near the coast indicate a stress concentration at the plate's interface at 38°S which might in part be induced by the fragmented forearc structure. Y1 - 2006 U6 - https://doi.org/10.1029/2006GL028189 SN - 0094-8276 VL - 33 IS - 23 PB - Union CY - Washington ER - TY - JOUR A1 - Palo, Mauro A1 - Tilmann, Frederik A1 - Krüger, Frank A1 - Ehlert, Lutz A1 - Lange, Dietrich T1 - High-frequency seismic radiation from Maule earthquake (M-w 8.8, 2010 February 27) inferred from high-resolution backprojection analysis JF - Geophysical journal international N2 - We track a bilateral rupture propagation lasting similar to 160 s, with its dominant branch rupturing northeastwards at about 3 kms(-1). The area of maximum energy emission is offset from the maximum coseismic slip but matches the zone where most plate interface aftershocks occur. Along dip, energy is preferentially released from two disconnected interface belts, and a distinct jump from the shallower belt to the deeper one is visible after about 20 s from the onset. However, both belts keep on being active until the end of the rupture. These belts approximately match the position of the interface aftershocks, which are split into two clusters of events at different depths, thus suggesting the existence of a repeated transition from stick-slip to creeping frictional regime. KW - Earthquake source observations KW - Wave propagation KW - Subduction zone processes Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggu311 SN - 0956-540X SN - 1365-246X VL - 199 IS - 2 SP - 1058 EP - 1077 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Lange, Dietrich A1 - Bedford, J. R. A1 - Moreno, M. A1 - Tilmann, F. A1 - Báez, Juan Carlos A1 - Bevis, M. A1 - Krüger, Frank T1 - Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011 JF - Geophysical journal international N2 - We focus on the relation between seismic and total postseismic afterslip following the Maule M-w 8.8 earthquake on 2010 February 27 in central Chile. First, we calculate the cumulative slip released by aftershock seismicity. We do this by summing up the aftershock regions and slip estimated from scaling relations. Comparing the cumulative seismic slip with afterslip modelswe showthat seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints. As the afterslip model implicitly contains the displacements from the aftershocks, this reflects the tendency of afterslip models to smear out the actual slip pattern. However, it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor. This effect, seen weakly for the Maule 2010 and also for the Tohoku 2011 earthquake, can be explained by taking into account the uncertainties of the seismicity and afterslip models. In spite of uncertainties, the hypocentral region of the Nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically. Therefore, these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture. In a second step, we divide the megathrust of the Maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time. We then compare this number to a time-dependent afterslip model by defining the 'afterslip to aftershock ratio' (ASAR) for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count. Although we find a linear relation between afterslip and aftershocks for most cells, there is significant variability in ASAR in both the downdip and along-strike directions of the megathrust. We compare the spatial distribution of ASAR with the spatial distribution of seismic coupling, coseismic slip and Bouguer gravity anomaly, and in each case we find no significant correlation. KW - Creep and deformation KW - Earthquake dynamics KW - Seismicity and tectonics KW - Continental margins: convergent Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggu292 SN - 0956-540X SN - 1365-246X VL - 199 IS - 2 SP - 784 EP - 799 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Lange, Dietrich A1 - Tilmann, Frederik A1 - Barrientos, Sergio E. A1 - Contreras-Reyes, Eduardo A1 - Methe, Pascal A1 - Moreno, Marcos A1 - Heit, Ben A1 - Agurto, Hans A1 - Bernard, Pascal A1 - Vilotte, Jean-Pierre A1 - Beck, Susan T1 - Aftershock seismicity of the 27 February 2010 Mw 8.8 Maule earthquake rupture zone JF - Earth & planetary science letters N2 - On 27 February 2010 the M-w 8.8 Maule earthquake in Central Chile ruptured a seismic gap where significant strain had accumulated since 1835. Shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity. Here, we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines. By processing the seismic data between 15 March and 30 September 2010 from stations from IRIS, IPGP, GFZ and University of Liverpool we determined 20,205 hypocentres with magnitudes M-w between 1 and 5.5. Seismic activity occurs in six groups: 1.) Normal faulting outer rise events 2.) A shallow group of plate interface seismicity apparent at 25-35 km depth and 50-120 km distance to the trench with some variations between profiles. Along strike, the aftershocks occur largely within the zone of coseismic slip but extend similar to 50 km further north, and with predominantly shallowly dipping thrust mechanisms. Along dip, the events are either within the zone of coseismic slip, or downdip from it, depending on the coseismic slip model used. 3.) A third band of seismicity is observed further downdip at 40-50 km depth and further inland at 150-160 km trench perpendicular distance, with mostly shallow dipping (similar to 28 degrees) thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture, and presumably above the intersection of the continental Moho with the plate interface. 4.) A deep group of intermediate depth events between 80 and 120 km depth is present north of 36 degrees S. Within the Maule segment, a large portion of events during the inter-seismic phase originated from this depth range. 5.) The magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the M-w 8.8 Maule 2010 earthquake. 6.) Pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of Pichilemu (similar to 34.5 degrees S). These crustal events occur in a similar to 30 km wide region with sharp inclined boundaries and oriented oblique to the trench. The best-located events describe a plane dipping to the southwest, consistent with one of the focal planes of the large normal-faulting aftershock (M-w = 6.9) on 11 March 2010. KW - Maule 2010 earthquake KW - local seismicity KW - aftershock distribution KW - subduction zone KW - Central Chile KW - seismogenic zone Y1 - 2012 U6 - https://doi.org/10.1016/j.epsl.2011.11.034 SN - 0012-821X VL - 317 IS - 2 SP - 413 EP - 425 PB - Elsevier CY - Amsterdam ER -