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| Titel |
Earthquake statistics, spatiotemporal distribution of foci and source mechanisms - a key to understanding of the West Bohemia/Vogtland earthquake swarms |
| VerfasserIn |
Josef Horalek, Hana Čermáková, Tomáš Fischer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126838
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| Publikation (Nr.) |
 EGU/EGU2016-6624.pdf |
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| Zusammenfassung |
| Earthquake swarms are sequences of numerous events closely clustered in space and
time and do not have a single dominant mainshock. A few of the largest events
in a swarm reach similar magnitudes and usually occur throughout the course of
the earthquake sequence. These attributes differentiate earthquake swarms from
ordinary mainshock-aftershock sequences. Earthquake swarms occur worldwide,
in diverse geological units. The swarms typically accompany volcanic activity at
margins of the tectonic plate but also occur in intracontinental areas where strain from
tectonic-plate movement is small. The origin of earthquake swarms is still unclear. The
swarms typically occur at the plate margins but also in intracontinental areas. West
Bohemia-Vogtland represents one of the most active intraplate earthquake-swarm areas in
Europe. It is characterised by a frequent reoccurrence of ML < 4.0 swarms and by
high activity of crustal fluids. West Bohemia-Vogtland is one of the most active
intraplate earthquake-swarm areas in Europe which also exhibits high activity of crustal
fluids. The Nový Kostel focal zone (NK) dominates the recent seismicity, there
were swarms in 1997, 2000, 2008 and 20011, and a striking non-swarm activity
(mainshock-aftershock sequences) up to magnitude ML= 4.5 in May to August 2014. The
swarms and the 2014 mainshock-aftershock sequences are located close to each
other at depths between 6 and 13 km. The frequency-magnitude distributions of all
the swarms show bimodal-like character: the most events obey the b-value = 1.0
distribution, but a group of the largest events depart significantly from it. All the
ML > 2.8 swarm events are located in a few dense clusters which implies step by
step rupturing of one or a few asperities during the individual swarms. The source
mechanism patters (moment-tensor description, MT) of the individual swarms indicate
several families of the mechanisms, which fit well geometry of respective fault
segments. MTs of the most events signify pure shears except for the 1997-swarm events
the MTs of which indicates a combine sources including both shear and tensile
components. The origin of earthquake swarms is still unclear. Nevertheless, we infer that
the individual earthquake swarms in West Bohemia-Vogtland are mixture of the
mainshock-aftershock sequences which correspond to step by step rupturing of one or a few
asperities. The swarms occur on short fault segments with heterogeneous stress
and strength, which may be affected by pressurized crustal fluids reducing normal
component of the tectonic stress and lower friction. This way critically loaded faults are
brought to failure and the swarm activity is driven by the differential local stress. |
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