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«Aktuelle Entwicklungen im BGR-Fachbereich Seismologisches Zentralobservatorium, Kernwaffenteststopp Christian Bönnemann Bundesanstalt für ...»

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Aktuelle Entwicklungen im BGR-Fachbereich "Seismologisches Zentralobservatorium,

Kernwaffenteststopp"

Christian Bönnemann

Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover

Der Schwerpunkt der Aufgaben des BGR-Fachbereichs B4.3 (Seismologisches Zentralobservatorium, Kernwaffenteststopp) liegt im Feld der Seismologie. An erster Stelle ist die Wahrnehmung

der Aufgabe des Erdbebendienst des Bundes zu nennen, der seine Daten vor allem von den Stationen des Deutsche Seismologische Regionalnetz (Betrieb in Zusammenarbeit mit Hochschulen, GFZ Potsdam und Landeserdbebendiensten), des Gräfenberg- und des GERESS-Arrays bezieht.

Für Verifikations des Kernwaffenteststoppvertrags (CTBT) ist das Nationale Datenzentrum in B4.3 angesiedelt. Auch hier spielt die Seismologie eine Schlüsselrolle, sowohl methodisch als auch durch die Synergie mit dem Datenzentrum des Seismologischen Zentralobservatoriums.

Stetig zugenommen hat in den letzten Jahren die fachliche Beratung und Forschung auf dem Gebiet der induzierten Seismizität. Neben der tiefen Geothermie und der Erdgasförderung ist auch das Fracking als mögliche Ursache von Erdbeben in den gesellschaftlichen Blickpunkt geraten.

Über die Seismologie hinaus befasst sich B4.3 mit dem Themenfeld Infraschall. Insbesondere bei der Digitalisierung, Übertragung und Archivierung der Daten lassen sich viele Herangehensweisen übertragen, während bei der Aufnahme und Auswertung der Messdaten meist andere Ansätze erforderlich sind. Infraschall ist ein recht neues und sich stürmisch entwickelndes Gebiet, das zahlreiche interessante Herausforderungen bietet.

Als jüngstes Aufgabenfeld ist zum Fachbereich der geophysikalische Anteil des GEOTHERMProgramms hinzugekommen. Dieses Programm wird vom Bundesministerium für wirtschaftliche Zusammenarbeit und Entwicklung finanziert und hat zum Ziel, in Partnerländern der Entwicklungszusammenarbeit die Nutzung geothermischer Energie zu fördern, wobei der Schwerpunkt in der Hochenthalpie-Geothermie liegt. Daher liegen die Arbeitsschwerpunkte in vulkanischen Regionen.

Um die Beratungsaufgaben mit der notwendigen Fachkompetenz flankieren zu können, wird zweckorientierte Drittmittelforschung betrieben, wobei die Finanzierung durch Mittelgeber wie DFG, EU, Land Niedersachsen oder DGMK erfolgt.

Downhole Seismic Monitoring in the Istanbul/Eastern Sea of Marmara Region: Recent Results from the ICDP-GONAF Project Marco Bohnhoff1,2, Georg Dresen1, Fatih Bulut1, Christina Raub1, Tugbay Kilic3, Recai F. Kartal3, Filiz Tuba Kadirioglu3, Murat Nurlu3, Peter E. Malin4, Hisao Ito5 GFZ German Research Center for Geosciences, Helmholtz-Centre Potsdam, Germany Freie Universität Berlin, Department of Earth Sciences, Germany.

AFAD, Disaster and Emergency Management Presidency, Earthquake Department, Ankara, Turkey.

Institute of Earth Science and Engineering, University of Auckland, Auckland, New Zealand.

Jamstec, Center for Deep Earth Exploration (CDEX), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanagawa, Japan.

The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara represents a ‘seismic gap’ where a major earthquake is expected to occur in the near future. The Marmara segment of the NAFZ is located between the 1912 Ganos and 1999 Izmit ruptures and is the only segment that has not ruptured since 1766. The ICDP-GONAF project (Geophysical Observatory at the North Anatolian Fault;

www.gonaf.de) involves the installation of a high-resolution borehole seismic observatory at the NAFZ consisting of several 300m deep vertical boreholes in the broader Istanbul / eastern Sea of Marmara region to monitor the Princes Islands segment at the transition from the ‘seismic gap’ to the recent 1999 Izmit rupture. GONAF is an international collaboration and co-funded by the International Continental Scientific Drilling Programme (ICDP), GFZ Potsdam and the Disaster and Emergency Management Presidency in Ankara/Turkey (AFAD). Further principal partners are IESE/New Zealand, JAMSTEC/Japan, MIT and UNAVCO/both US,. The principal scientific objective of GONAF is to study physical processes acting before, during and after the expected M7 earthquake along the Princes Islands segment by long-term monitoring microseismic activity at significantly reduced magnitude detection threshold and improved hypocentral resolution. By the end of 2013 three GONAF boreholes were successfully implemented and arrays of borehole seismometers were installed for permanent operation. Vertical 1Hz seismometers at 75m spacing as well as several different 3component borehole seismometers at 300m depth are installed and are completed by a set of surface sensors. The benefit of seismic waveforms recorded at depth in a low-noise environment is shown and first results of microseismic activity along the Princes Islands segment are presented and will be discussed in the seismotectonic context.

Spatial distribution of scattering and absorption features revealed by coda waves from intermediate depth earthquakes in Vrancea region (Romania) (1, 2) (3) (1) (2) (2) F. Borleanu, L. De Siena, C. Thomas, M. Popa, M. Radulian Institute for Geophysics, University of Munster (Germany) National Institute for Earth Physics (Romania) School of Geosciences, University of Aberdeen (Scotland) The Vrancea region, located at the limit of the SE Carpathians arc, is one of the regions of notable seismicity in Europe whose major earthquakes affect a large part of the SE Europe. Despite the numerous seismological and geodynamical studies, which provided a significant amount of new results and interpretations, this peculiar region is still subject to numerous controversies and debates. In the present study our goal is to investigate seismic coda wave attenuation in the Vrancea region and adjacent areas using data recorded by the broadband stations of the Romanian Seismic Network and produced by intermediate depth earthquakes that occurred mostly between 2009 and 2011. We select waveforms with a signal to noise ratio (SNR) larger than 1.5 where we measure peak delay times (Tpd) in four frequency ranges, where Tpd are defined as the time-difference between the S-wave travel time and the maximum amplitude of the envelope. In our approximation, this parameter characterizes the scattering due to heterogeneities present along the propagation path, while the coda quality factor (Qc - measured from the exponential decrease of coda waves at large lapse-times) is a measure of absorption. We subsequently applied a cluster analysis to the results in order to get an interpretation in terms of intrinsic and scattering attenuation. The results show that the peak delay times exhibit a different behavior, especially at low frequencies, relative to other geographical regions investigated in literature. Scattering is more pronounced NW of Vrancea, while absorption is prevalent in the Focsani Basin, located in the forearc region. We obtain lower absorption in stable regions, and an opposite behaviour in regions characterized by active seismicity and structural heterogeneity.





SEISMOLOGICAL ANALYSIS OF THE 1917 MONTERCHI EARTHQUAKE (ITALY)

Thomas Braun (1), Marco Caciagli (1,2) und Simone Cesca (3) (1) INGV-Arezzo, (2) INGV-Bologna, (3) GFZ-Potsdam The seismotectonics of the Upper Tiber Valley are dominated by the Altotiberina Fault (ATF), an NE-dipping low-angle normal fault system, and its antithetic W-dipping high-angle normal faults, both active at least since the Late Pliocene (Barchi, et al., 2009, Boncio et al., 2000). Although the southern part of the ATF was demonstrated to creep (Piccinini et al., 2003), its capability to generate strong or moderate earthquakes is still under debate and – to this date – the main regional historical seismic events could not be associated to specific geologic sources.

On April 26, 1917 at 9:35:59 (GMT) a strong earthquake struck the northernmost portion of the Upper Tiber Valley (Tuscany) producing severe damages and about 20 fatalities. The Catalogue of Strong Italian Earthquakes (Boschi et al., 2000) reports this event as the so-called Monterchi earthquake, relating to 134 macroseismic observations, mainly distributed on the western side of the Tiber Valley. The maximum and epicentral intensity was determined as Io=IX-X (MCS), corresponding to an equivalent magnitude of Me=6, that defines this event as the most important of the area. A detailed study of the Monterchi earthquake is of great actual importance not only for a better understanding of the seismotectonics and the related seismic hazard of the area, but especially concerning the question whether a LANF is capable to generate strong earthquakes.

A total of 49 historical seismograms from 19 different Euro-Mediterranean observatories are available in the database of the SISMOS Project - INGV (http://sismos.rm.ingv.it/). The BAAS bulletin (British Association for Advancement of Sciences) of 1917, although if incomplete because of the 1st World War, reports a list of 21 seismological observatories that recorded the P and Sphases for this earthquake (Caciagli et al., 2006). We included additional arrival-times deriving from further seismic bulletins - not contained in the BAAS reports - and from digitalizing original historical seismograms. We obtain a new, robust and consistent hypocentral solution, coherent with the macroseismic data, in particular by using S-P travel time differences for recordings where the absolute timing is uncertain.

An accurate research on the technical characteristics of the recording historical seismometers (period, damping, gain etc.), allowed to deconvolve the original digitalized seismic traces (i) to determine the main seismic parameters (Mo, Mw, Circular Fault Radius), (ii) to constrain the possible source mechanism, by a combination of first motion analysis and modelling of synthetic seismograms (seismosizer), and (iii) to implement the solution in the framework of the regional tectonic setting (Caciagli et al., 2014).

REFERENCES

Barchi MR, et al. (2009): Seismic images of an extensional basin, generated at the hanging-wall of a low-angle normal fault: The case of the Sansepolcro basin (Central Italy), Tectonophysics, 479 (3-4): 285-293.

Boncio P, et al. (2000): Architecture and seismotectonics of a regional Low-Angle Normal Fault Zone in Central Italy.

Tectonics, 19: 1038-1055.

Boschi E, et al. (2000): Catalogue of Strong Italian Earthquakes from 461 B.C. to 1997 (Appendix to volume 43 N° 4, 2000), Annals of Geophysics, 43 (4).

Caciagli M, et al. (2006): The “Alta Val Tiberina" (Italy) earthquake of 26 th April 1917: Reassessment of the main seismological parameters, Act of 1st European Conference on Earthquake Engineering and Seismology, Geneva, Switzerland, 3-8 September 2006, Geneva, Switzerland, 104-105.

Caciagli M et al., (2014): Seismological analysis of the 1917 Monterchi Earthquake (Central Apennines, Italy) for seismotectonic implications. Proc. 34 ESC-Conference, Istanbul 24-29.8.2014.

Piccinini D, et al. (2003): A microseismic study in a low seismicity area of Italy: the Città di Castello 2000-2001 experiment. Annals of Geophysics, 46 (6): 1315-1324.

The 2012 Ahar-Varzeghan earthquake doublet (Mw 6.4 and 6.2) – rupture on the same or conjugate faults?

S. Donner, H. Sudhaus, A. Ghods, F. Krüger, D. Rößler, A. Landgraf, P. Ballato

The region of northwestern Iran is exceptional within the Arabian-Eurasian continental collision zone. The recent tectonic activity seems to be dominated by the NW-SE striking right-lateral North Tabriz Fault (NTF) where regional seismicity (historical and modern one) concentrates. North of the NTF seismicity is rare and very little is known about active structures so far. Here, GPS velocity vectors are pointing North-East, while south of the NTF this direction changes to direct North.

On 11th of August 2012 the region was unsuspectedly struck by a shallow Mw 6.4 earthquake with a pure right-lateral strike-slip mechanism, which occurred about 50 km north of the NTF. Only 11 minutes later and about 6 km further NW a second shallow event with Mw 6.2 occurred. It showed an NE-SW oriented oblique thrust mechanism. Field observations revealed an E-W striking, about 12 km long surface rupture west of the first event.

While for the first event rupture on a E-W oriented fault is evident, the identification of the rupture plane for the second event is ambigious. So far, different authors assume an ENE-WSW oriented fault plane. This assumption implies rupture of the same fault by both events. However, there are several indications that challenge this theory: 1. A theoretical mechanism based on the dimension and geometry of the surface rupture would be identical with the mechanism of the first event. An additional thrust component activated during the second event seems at odds with this fault. 2. The aftershock sequence somewhat north of the source area outlines activated, N-S oriented structures. So, a N-S rupture plane for the second event seems to be quite possible.

By inverting regional waveform data for the eikonal source and surface displacement measurements from satellite InSAR data plus additional information from geology and tectonics we test if a NNE-SSW oriented fault plane could explain the observations similarly well than the so far postulated EW-oriented fault plane. We look into directivity effects of the second event, which seem to support a NNE-SSW oriented fault plane for the second event, and furthermore employ SAR data. In the presentation we show preliminary results and discuss some technical difficulties that arise when studying this particular earthquake doublet or earthquakes sequences in general.

Preparing the installation of station ELYS: The InSight mission Brigitte Knapmeyer-Endrun, Max Planck Institute for Solar System Reseach (MPS), Göttingen NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission to Mars is expected to place a seismometer on the surface of the planet in the Elysium Planitia region in September 2016. If successful, this station, already registered with code ELYS at IRIS, will provide the first ever recordings of seismic events on Mars and address a number of important scientific questions on the structure, composition, present-day seismic and volcanic activity of the planet, and meteorite influx.



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