57 documents found in 137ms
# 51
Heit, Benjamin • Yuan, Xiaohui • Mancilla, Flor de Lis
Abstract: We operated a densely spaced broadband seismic field experiment to study the structure of the crust and mantle lithosphere across the Sierra Nevada mountain range, southern Spain. The Sierra Nevada is one of the key areas within the complicated Betic-Alboran-Rif system. It contains the highest mountain of the Iberian Peninsula and is located in the close vicinity of a very deep seismic zone (>600 km depth). This region plays a decisive role in answering the question if subduction or delamination is the dominant geological process in the western Mediterranean. The seismic array, consisting of 40 broadband stations spaced 2 km apart (compared to earlier station spacing of ~50 km), has been deployed in September 2010 by a joint effort of GFZ Potsdam and University of Granada, and has been operated until the end of 2011. The proposed scientific work is the analysis of the data collected with the present experiment which includes mainly P and S receiver function analysis and surface wave tomography with ambient noise data. We will image the seismic structure and thickness variation of the crust and mantle lithosphere at high resolution and hence infer tectonic and geodynamic processes related to the Africa-Eurasia collision. The resulting structural details especially of the mantle lithosphere will contribute essentially to the recognition of the geodynamic deformations in the western part of the African-Eurasian plate collision. Data are available from the GFZ seismological data archive.
# 52
Yuan, Xiaohui • Mechie, James • Schurr, Bernd
Abstract: We study deep structures and geodynamic processes in the Tien Shan and Pamir collision zones, central Asia, with passive source seismic experiments in Kyrgyzstan and Tajikistan. In 2008, a total of 40 seismic stations were deployed predominantly along a 350 km long N-S profile and partly as a sparse 2D seismic network covering an area of 300x300 km of the central Pamir plateau. In 2009, the array was rearranged into a 2D network with higher station density. The proposed scientific tasks to study the crust and upper mantle with seismic methods include (i) teleseismic P and S receiver functions, (ii) shear wave splitting, (iii) location of local earthquakes and waveform inversion for source mechanism, (iv) seismic tomography using local and teleseismic earthquakes, and (v) tomography of surface waves and ambient noise.
# 53
Heit, Benjamin • Yuan, Xiaohui • Kind, Rainer • Asch, Günter
Abstract: The seismic array is part of a collaborative international passive-source seismic experiment in the southern Puna (25°S to 28°S) that aims to address fundamental questions on the processes that form, modify and destroy continental lithosphere and control lithospheric dynamics along Andean-type continental margins. The southern Puna is anomalous with respect to the rest of the Andean plateau in having a distinct magmatic and structural history, a large deficit in crustal shortening compared to its elevation and an underlying slab with a transitional dip between a steeper segment to the north and the Chilean flat-slab to the south. With the international project we proposed to test the hypothesis of the lithospheric delamination beneath the southern Puna. The total network consists of 75 seismic stations and has been operated in Argentina and chile for 2 years. The GFZ has contributed 30 stations with EarthData logger (EDL). Sensors include broadband Güralp 3ESP (60 s) and 3T (100 s) and short-period Mark L4 (1 s). Continuous data are freely available on the GEOFON. The US data can be requested from the IRIS.
# 54
Passarelli, Luigi • Roessler, Dirk • Aladino, Govoni • Maccaferri, Francesco • Moretti, Milena • (et. al.)
Abstract: The temporary Pollino Seismic Experiment, FDSN network code 4A, monitored the earthquake swarm in the Pollino Range region, Italy, between November 2012 and September 2014. The region is located at the transition from the Southern Apennines chain to the Calabrian arc. Striking a volume of about 20x20x15 km, the swarm started in October 2010, culminated in an Mw=5.2 event on 25 October 2012, and has continued since with a variable rate of activity. The area represents a seismic gap as there are no documented historical M>6 earthquakes during the last thousand years. The tectonic structures of the area are poorly known. The experiment was part of a collaborative effort made by the German Research Centre for Geosciences (GFZ) and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) within the framework of the NERA and CCMP-Pompei projects. The 4A network consisted of 9 stations including 6 short-period and 3 broadband instruments, provided by GFZ. The permanent seismic network was complemented by the 9 GFZ stations and 5 IV stations temporarily installed by INGV. The short-period stations had Mark L-4C3D sensors with EDL digitizers. The broadband stations were equipped with STS2.5 seismometers and RefTek RT130S digitizers. Five short period and one broadband (CSA0 to CSA5) were installed in a small-aperture array in the west of the range. The other three stations (broadband: CSB, CSC and short period: CSD) were installed around the swarm area. The array and the network stations recorded in continuous mode at 200 Hz and at 100 Hz, respectively. The sensors were buried in the ground at 0.5 m depth except for CSB and CSD which were installed on the surface. High-precision station coordinates were obtained by using differential GPS measurements. The data have been used to analyze the earthquakes and seismogenetic structures and to discern the characteristics of the swarm sequence.
# 55
Roessler, Dirk • Hiemer, Stefan • Bach, Christoph • Delavaud, Elise • Krueger, Frank • (et. al.)
Abstract: Earthquake swarms occur frequently in Vogtland/West Bohemia at the German-Czech border. The link between these earthquakes and magmatic fluids that escape at the surface has been debated and investigated. The Rohrbach/Vogtland seismic array, installed by the University of Potsdam, Germany, was a small-aperture array that monitored the major earthquake swarm in 2008 and the background seismicity between October 16, 2008 and March 18, 2009. The array consisted of 11 stations equipped with MarsLite data loggers and Lennartz Le3D-5s seismometers. Data were recorded in continuous mode at 250 Hz. Sensors were buried in the ground at 0.5 m depth. High-precision station coordinates were obtained using differential GPS measurements. The array data has been used for analyses of earthquakes and seismic structures. Waveform data is fully open.
# 56
Ryberg, Trond • Haberland, Christian
Abstract: The Toba caldera is located in north Sumatra, Indonesia. It is part of the volcanic arc associated with the subduction of the Australian Plate beneath the Southeast-Asian Plate. The subduction zone, and the Sumatra Fault, a right lateral strike-slip fault which marks the plate boundary, are seismically active. In order to investigate the volcano-related seismic activity and image the volcano related structures (i.e. a potential magma chamber) using ambient noise techniques a dense seismic network was installed around Lake Toba between May and October 2008. The network, deployed within a German-Indonesian cooperation, comprised 42 continuously recording seismic stations equipped with three-component, short-period seismic sensors with 1 Hz natural frequency. The GPS-synchronised data loggers recorded at 100 samples per second for the experiment's time span of 6 months. During this time period local and regional seismicity was recorded. The array of stations covers an area of approx. 150 by 200 km with inter-station distances of about 20 km. The station distribution is quite irregular due to the difficult environmental conditions. Data from all stations are freely available from the GFZ seismological data archive.
# 57
Heit, Ben • Yuan, Xiaohui • Jokat, Wilfried • Weber, Michael • Geissler, Wolfram
Abstract: The Etendeka continental flood-basalt province in northern Namibia, linked by the Walvis Ridge to the Tristan da Cunha hotspot, has great importance in global plate tectonic concepts, and is an ideal place to understand the role of the plume-lithosphere interaction during the break-up of the Southern Atlantic Ocean. Within this frame we operated an amphibian passive-source seismic network (WALPASS for Walvis Ridge Passive Source Experiment) in the region where the Walvis Ridge intersects with the continental margin of northern Namibia. The land network operated for over two years while the OBS stations were in operation for one year. The broadband seismic network is composed of 28 three-component land stations and 12 ocean-bottom stations. This configuration of stations will allow us to map the lithospheric and upper mantle structure in the ocean-continent transition beneath the passive continental margin of northern Namibia and to examine possible seismic anomalies related to the postulated hotspot track from the continent to the ocean along the Walvis Ridge. The acquired data should help clarify the velocity anomaly in the lowermost mantle caused by the Africa super plume and to improve the distribution of seismicity in this geophysically little studied region.
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