TY - GEN A1 - Donner, Stefanie A1 - Rößler, Dirk A1 - Krüger, Frank A1 - Ghods, Abdolreza A1 - Strecker, Manfred T1 - Source mechanisms of the 2004 Baladeh (Iran) earthquake sequence from Iranian broadband and short-period data and seismotectonic implications N2 - The northward movement and collision of the Arabian plate with Eurasia generates compressive stresses and resulting shortening in Iran. Within the Alborz Mountains, North Iran, a complex and not well understood system of strike-slip and thrust faults accomodates a fundamental part of the NNE-SSW oriented shortening. On 28th of May 2004 the Mw 6.3 Baladeh earthquake hit the north-central Alborz Mountains. It is one of the rare and large events in this region in modern time and thus a seldom chance to study earthquake mechanisms and the local ongoing deformation processes. It also demonstrated the high vulnerability of this densily populated region. KW - Momententensoren KW - Inversion KW - Baladeh KW - Iran KW - moment tensors KW - inversion KW - Baladeh KW - Iran Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53982 ER - TY - GEN A1 - Rößler, Dirk A1 - Hiemer, Stephan A1 - Bach, Christoph A1 - Delavaud, Elise A1 - Krüger, Frank A1 - Ohrnberger, Matthias A1 - Sauer, David A1 - Scherbaum, Frank A1 - Vollmer, Daniel T1 - Small-aperture seismic array monitors Vogtland earthquake swarm in 2008/09 N2 - The most recent intense earthquake swarm in the Vogtland lasted from 6 October 2008 until January 2009. Greatest magnitudes exceeded M3.5 several times in October making it the greatest swarm since 1985/86. In contrast to the swarms in 1985 and 2000, seismic moment release was concentrated near swarm onset. Focal area and temporal evolution are similar to the swarm in 2000. Work hypothysis: uprising upper-mantle fluids trigger swarm earthquakes at low stress level. To monitor the seismicity, the University of Potsdam operated a small aperture seismic array at 10 km epicentral distance between 18 October 2008 and 18 March 2009. Consisting of 12 seismic stations and 3 additional microphones, the array is capable of detecting earthquakes from larger to very low magnitudes (M<-1) as well as associated air waves. We use array techniques to determine properties of the incoming wavefield: noise, direct P and S waves, and converted phases. KW - Vogtland KW - Erdbebenschwarm 2008 KW - Arrayseismologie KW - Vogtland KW - West Bohemia KW - earthquake swarm KW - array seismology Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-29185 ER - TY - GEN A1 - Donner, Stefanie A1 - Strecker, Manfred A1 - Rößler, Dirk A1 - Ghods, Abdolreza A1 - Krüger, Frank A1 - Landgraf, Angela A1 - Ballato, Paolo T1 - Earthquake source models for earthquakes in Northern Iran N2 - The complex system of strike-slip and thrust faults in the Alborz Mountains, Northern Iran, are not well understood yet. Mainly structural and geomorphic data are available so far. As a more extensive base for seismotectonic studies and seismic hazard analysis we plan to do a comprehensive seismic moment tensor study also from smaller magnitudes (M < 4.5) by developing a new algorithm. Here, we present first preliminary results. KW - Elburs KW - Iran KW - Momententensor KW - Seismotektonik KW - Alborz KW - Iran KW - moment tensor KW - seismotectonics Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-32581 ER - TY - GEN A1 - Krüger, Frank A1 - Ohrnberger, Matthias A1 - Rößler, Dirk T1 - Rupture imaging of large earthquakes with a poststack isochrone migration method N2 - Rapid and robust characterization of large earthquakes in terms of their spatial extent and temporal duration is of high importance for disaster mitigation and early warning applications. Backtracking of seismic P-waves was successfully used by several authors to image the rupture process of the great Sumatra earthquake (26.12.2004) using short period and broadband arrays. We follow here an approach of Walker et al. to backtrack and stack broadband waveforms from global network stations using traveltimes for a global Earth model to obtain the overall spatio-temporal development of the energy radiation of large earthquakes in a quick and robust way. We present results for selected events with well studied source processes (Kokoxili 14.11.2001, Tokachi-Oki 25.09.2003, Nias 28.03.2005). Further, we apply the technique in a semi-real time fashion to broadband data of earthquakes with a broadband magnitude >= 7 (roughly corresponding to Mw 6.5). Processing is based on first automatic detection messages from the GEOFON extended virtual network (GEVN). KW - Seismologie KW - Erdbeben KW - Array Seismologie KW - Migration KW - Seismology KW - Earthquake KW - Array Seismology KW - Migration Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18395 ER - TY - GEN A1 - Lipke, Katrin A1 - Krüger, Frank A1 - Rößler, Dirk T1 - Subduction zone structure along Sumatra from receiver functions N2 - Receiver functions are a good tool to investigate the seismotectonic structure beneath the a seismic station. In this study we apply the method to stations situated on or near Sumatra to find constraints on a more detailed velocity model which should improve earthquake localisation. We estimate shallow Moho-depths (~ 21 km) close to the trench and depths of ~30 km at greater distances. First evidences for the dip direction of the slab of ~60° are provided. Receiver functions were calculated for 20 stations for altogether 110 earthquakes in the distance range between 30° and 95° from the receiver. However the number of receiver functions per station is strongly variable as it depends on the installation date, the signal-to-noise-ratio of the station and the reliability of the acquisition. N2 - Receiver Funkttion stellen eine gut Methode zur Untersuchung von Seismotektonischen Strukturen unterhalb einer seismischen Station dar. In dieser Arbeit wenden wir die Methode auf Station auf oder nahe Sumatra an um Hinweise für ein detaillierteres Geschwindigkeitsmodell zu erhalten, welches die Lokalisierung von Erdbeben verbessern sollte. Wir ermitteln flache Moho-Tiefen (~21 km) in der Nähe des Trenchs und Tiefen um die 30 km in größeren Distanzen. Erste Hinweise für eine Einfallsrichtung des Slabs von ~60° konnten gefunden werden. Receiver Funktionen wurden für 20 Stationen für insgesamt 110 Erdbeben im Distanzbereich zwischen 30° und 95° berechnet. allerdings ist die Anzahl von Receiver Funktionen pro Station sehr variabel, da sie vom Installationszeitpunkt, dem Signal-Rausch-Verhältnis und der Zuverlässigkeit der Datenaufnahme an der Station abhängt. KW - Receiver Funktionen KW - Sumatra KW - Seismologie KW - Subduktion KW - Receiver Functions KW - Sumatra KW - Seismology KW - Subduction Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18260 ER - TY - GEN A1 - Rößler, Dirk A1 - Krüger, Frank A1 - Ohrnberger, Matthias A1 - Ehlert, Lutz T1 - Automatic near real-time characterisation of large earthquakes N2 - An der Universität Potsdam wird seit 2008 ein automatisiertes Verfahren angewandt, um Bruchparamter großer Erdbeben in quasi-Echtzeit, d.h. wenige Minuten nachdem sich das Beben ereignet hat, zu bestimmen und der Öffentlichkeit via Internet zur Verfügung zu stellen. Es ist vorgesehen, das System in das Deutsch-Indonesische Tsunamifrühwarnsystem (GITEWS) zu integrieren, für das es speziell konfiguriert ist. Wir bestimmen insbesondere die Dauer und die Ausdehnung des Erdbebens, sowie dessen Bruchgeschwindigkeit und -richtung. Dabei benutzen wir die Seismogramme der zuerst eintreffenden P Wellen vom Breitbandstationen in teleseimischer Entfernung vom Beben sowie herkömmliche Arrayverfahren in teilweise modifizierter Form. Die Semblance wir als Ähnlichkeitsmaß verwendet, um Seismogramme eines Stationsnetzes zu vergleichen. Im Falle eines Erdbebens ist die Semblance unter Berücksichtigung des Hypozentrums zur Herdzeit und während des Bruchvorgangs deutlich zeitlich und räumlich erhöht und konzentriert. Indem wir die Ergebnisse verschiedener Stationsnetzwerke kombinieren, erreichen wir Unabhängigkeit von der Herdcharakteristik und eine raum-zeitliche Auflösung, die es erlaubt die o.g. Parameter abzuleiten. In unserem Beitrag skizzieren wir die Methode. Anhand der beiden M8.0 Benkulu Erdbeben (Sumatra, Indonesien) vom 12.09.2007 und dem M8.0 Sichuan Ereignis (China) vom 12.05.2008 demonstrieren wir Auflösungsmöglichkeiten und vergleichen die Ergebnisse der automatisierten Echtzeitanwendung mit nachträglichen Berechnungen. Weiterhin stellen wir eine Internetseite zur Verfügung, die die Ergebnisse präsentiert und animiert. Diese kann z.B. in geowissenschaftlichen Einrichtungen an Computerterminals gezeigt werden. Die Internetauftritte haben die folgenden Adressen: http://www.geo.uni-potsdam.de/arbeitsgruppen/Geophysik_Seismologie/forschung/ruptrack/openday http://www.geo.uni-potsdam.de/arbeitsgruppen/Geophysik_Seismologie/forschung/ruptrack KW - Erdbeben KW - Arrayseismologie KW - Echtzeitanwendung KW - teleseismische Bruchverfolgung KW - earthquake KW - array seismology KW - real-time application KW - teleseismic rupture tracking Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-20191 ER - TY - GEN A1 - Rößler, Dirk A1 - Krüger, Frank A1 - Ohrnberger, Matthias T1 - Automatic near real-time characterisation of large earthquakes N2 - We use seismic array methods (semblance analysis) to image areas of seismic energy release in the Sunda Arc region and world-wide. Broadband seismograms at teleseismic distances (30° ≤ Δ ≤ 100°) are compared at several subarrays. Semblance maps of different subarrays are multiplied. High semblance tracked over long time (10s of second to minutes) and long distances indicate locations of earthquakes. The method allows resolution of rupture characteristics important for tsunami early warning: start and duration, velocity and direction, length and area. The method has been successfully applied to recent and historic events (M>6.5) and is now operational in real time. Results are obtained shortly after source time, see http://www.geo.uni-potsdam.de/Forschung/Geophysik/GITEWS/tsunami.htm). Comparison of manual and automatic processing are in good agreement. Computational effort is small. Automatic results may be obtained within 15 - 20 minutes after event occurrence. KW - Seismology KW - Earthquake KW - Tsunami KW - Array Seismology Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18382 ER - TY - GEN A1 - Rößler, Dirk A1 - Krüger, Frank A1 - Ohrnberger, Matthias T1 - Rupture Propagation of the 2008/05/12 Ms8.0 Wenchuan Earthquake N2 - We study the rupture propagation of the 2008/05/12 Ms8.0 Wenchuan Earthquake. We apply array techniques such as semblance vespagram analysis to P waves recorded at seismic broadband station within 30-100° epicentral distance. By combination of multiple large aperture station groups spatial and temporal resolution is enhanced and problems due source directivity and source mechanism are avoided. We find that seismic energy was released for at least 110 s. Propagating unilaterally at sub-shear rupture velocity of about 2.5 km/s in NE direction, the earthquake reaches a lateral extent of more than 300 km. Whereas high semblance during within 70 s from rupture start indicates simple propagation more complex source processes are indicated thereafter by decreases coherency in seismograms. At this stage of the event coherency is low but significantly above noise level. We emphasize that first result of our computations where obtain within 30 minutes after source time by using an atomized algorithm. This procedure has been routinely and globally applied to major earthquakes. Results are made public through internet. KW - Sichuan KW - Wenchuan KW - Erdbeben KW - Bruchverfolgung KW - Arrayseismologie KW - Sichuan KW - Wenchuan KW - earthquake KW - rupture KW - propagation KW - array seismology Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-29195 ER - TY - GEN A1 - Rößler, Dirk A1 - Krüger, Frank A1 - Ohrnberger, Matthias T1 - Rupture propagation of recent large TsE off-coast Sumatra and Java N2 - The spatio-temporal evolution of the three recent tsunamogenic earthquakes (TsE) off-coast N-Sumatra (Mw9.3), 28/03/2005 (Mw8.5) off-coast Nias, on 17/07/2006 (Mw7.7) off-coast Java. Start time, duration, and propagation of the rupture are retrieved. All parameters can be obtained rapidly after recording of the first-arrival phases in near-real time processing. We exploit semblance analysis, backpropagation and broad-band seismograms within 30°-95° distance. Image enhancement is reached by stacking the semblance of arrays within different directions. For the three events, the rupture extends over about 1150, 150, and 200km, respectively. The events in 2004, 2005, and 2006 had source durations of at least 480s, 120s, and 180s, respectively. We observe unilateral rupture propagation for all events except for the rupture onset and the Nias event, where there is evidence for a bilateral start of the rupture. Whereas average rupture speed of the events in 2004 and 2005 is in the order of the S-wave speed (≈2.5-3km/s), unusually slow rupturing (≈1.5 km/s) is indicated for the July 2006 event. For the July 2006 event we find rupturing of a 200 x 100 km wide area in at least 2 phases with propagation from NW to SE. The event has some characteristics of a circular rupture followed by unilateral faulting with change in slip rate. Fault area and aftershock distribution coincide. Spatial and temporal resolution are frequency dependent. Studies of a Mw6.0 earthquake on 2006/09/21 and one synthetic source show a ≈1° limit in resolution. Retrieved source area, source duration as well as peak values for semblance and beam power generally increase with the size of the earthquake making possible an automatic detection and classification of large and small earthquakes. KW - Tsunami KW - Erdbeben KW - Indischer Ozean KW - Bruchausbreitung KW - Seismologie KW - Tsunami KW - Earthquake KW - Indonesia KW - Indian Ocean KW - Rupture Propagation KW - Seismology Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13039 ER -