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Titel |
Active Seismicity and Tectonics in Central Asia from Seismological Data Recorded in the Pamir and Tien Shan Mountain Ranges |
VerfasserIn |
Christian Sippl, Bernd Schurr, Felix M. Schneider, Xiaohui Yuan, James Mechie, Vladislav Minaev, Ulan A. Abdybachaev, Mustafo Gadoev, Ilhomjon Oimahmadov |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250034497
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Zusammenfassung |
Active tectonics in the Pamir mountains in central Asia, the westernmost part of the
India-Eurasia collision zone, are controlled by ongoing convergence (about 20 mm/yr),
causing substantial crustal shortening and compressional deformation. This leads to high
seismicity rates throughout the region. Whereas seismic activity along the rim of the
Pamir plateau is mostly compressional and concentrated along the Main Pamir
Thrust, the distribution and focal mechanisms of earthquakes in its interior are more
diffuse, with extensional events occurring along North-South trending rift zones
(Kara Kul, Wachan). Seismicity in the south-western Pamir and in the Hindu Kush
features frequent intermediate-depth earthquakes, reaching hypocentral depths of 300
km, which is rare for regions not obviously related to active subduction of oceanic
lithosphere. These mantle earthquakes, which are not observed beneath the Himalayas and
Tibet further east, form a rather well-defined Wadati-Benioff zone that was readily
interpreted as subducted lithosphere present below the current collisional orogen. Earlier
seismological studies showed the presence of a northward-dipping lithospheric
slab under the Hindu Kush and a southward-dipping one beneath the Pamirs, with
a small seismic gap in-between. Different hypotheses concerning the nature of
these slabs (oceanic or continental lithosphere) and tectonic geometry in general
(two slabs subducting in opposite directions or a single, hugely contorted slab)
have been proposed in literature. Political instability in the region in the last two
decades hampered on-site studies and field work, leaving many key issues poorly
understood.
In the framework of the multidisciplinary project TIPAGE (Tien Shan Pamir Geodynamic
Programme), for the first time, new field campaigns collecting high quality data have
been made possible. Local seismicity in the Pamir and Tien Shan mountain ranges
(Tajikistan and Kyrgyzstan) is currently being recorded by a temporary installation
of 40 seismic stations, 30 in Tajikistan and 10 in Kyrgyzstan, for a total time of
two years starting summer 2008. In 2009, the configuration of the stations was
changed from a 24-station North-South profile plus 16 additional stations distributed
throughout the Pamirs to a 40-station 2D setup evenly covering the whole study region.
Moreover, the first half of the data was retrieved, for which we will present preliminary
results. The high density of seismic stations allows precise location of earthquake
hypocenters and determination of source mechanisms for selected events. So far
we detected some 10,000 events, a significant proportion of which are related to
aftershocks of a Mw 6.6 earthquake that occurred in October 2008 in the border
triangle of Kyrgyzstan, Tajikistan and China, directly beneath one of our stations. The
hypocenter distribution of a selection of detected events provides a good indication on
active faults in the region, thus enabling us to interpret ongoing tectonic activity. We
will also present seismicity cross-sections through interesting subparts of the study
region that will shed a new light on the complex geometry of mantle deformation. |
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