HR: 09:30h
AN: S11C-07    [Abstracts]
TI: Intracontinental Swarm Earthquake Areas in Central Europe Compared with Areas in Africa and America
AU: * Klinge, K
EM: klinge@szgrf.bgr.de
AF: Federal Institute for Geosciences and Natural Resources (BGR), Central Seismological Observatory Graefenberg (SZGRF), Mozart Str. 57, Erlangen, 91052 Germany
AU: Stammler, K
S11C-07 AF: Federal Institute for Geosciences and Natural Resources (BGR), Central Seismological Observatory Graefenberg (SZGRF), Mozart Str. 57, Erlangen, 91052 Germany
AU: Ibs-von Seht, M
S11C-07 AF: Federal Institute for Geosciences and Natural Resources (BGR), Central Seismological Observatory Graefenberg (SZGRF), Mozart Str. 57, Erlangen, 91052 Germany
AU: Plenefisch, T
S11C-07 AF: Federal Institute for Geosciences and Natural Resources (BGR), Central Seismological Observatory Graefenberg (SZGRF), Mozart Str. 57, Erlangen, 91052 Germany
AB: The occurrence of earthquake swarms is typically related to magmatic activities of active volcanoes, yet swarms are also common for other intracontinental regions of increased geodynamic activity. Among these, the continental rifts play an important role. We present a summary of geophysical observations that have been made in swarm earthquake areas of the Vogtland/NW-Bohemia region in Central Europe and the Rio Grande and Kenya Rifts in America and Africa, respectively. Major similarities in the evolution, tectonism, and present-day lithospheric structure of the Rio Grande and Kenya Rifts are also reflected in the occurrence of earthquake swarms observed in the two rifts. In both rifts, swarms predominantly occur in those sections that are influenced by large-scale fracture zones intersecting the main course of the rifts. The earthquake swarms take place in the rift centres, mostly at shallow depth between 0 and 10km. The maximum magnitudes are mostly less than 4.5 and the b-values are about 0.8, hence not deviating from a normal non-volcanic intraplate environment. Focal mechanism studies give similar and uniform pictures of stress field orientation and faulting style for both rifts. There is no indication that swarm earthquakes in continental rifts can be characterised by a local and heterogeneous stress system as assumed for active volcanoes. Similar observations have been made for the Vogtland/NW-Bohemia swarm earthquake region. Here, large part of the swarm activity takes place at the intersection of the Marianske fault zone and the Eger graben which is part of the Cenozoic European rift system. Also depth range, magnitude statistics, and stress regime inferred from focal parameter investigations are comparable to those found for the American and African continental rift swarm areas. The occurrence of earthquake swarms in the Rio Grande and Kenya rifts is attributed to mid-crustal magma bodies beneath the graben axes. Evidence for the presence of magma bodies and related fluid movements that cause the earthquake swarms comes from various geophysical observations. It is discussed if a similar source can be assumed for the generation of the Vogtland/NW-Bohemia earthquake swarms.
DE: 7200 SEISMOLOGY
DE: 7205 Continental crust (1219)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005