@phdthesis{Roessler2006,
  author    = {R{\"o}ßler, Dirk},
  title     = {Retrieval of earthquake source parameters in inhomogeneous anisotropic mediawith application to swarm events in West Bohemia in 2000},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7758},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Earthquakes form by sudden brittle failure of rock mostly as shear ruptures along a rupture plane. Beside this, mechanisms other than pure shearing have been observed for some earthquakes mainly in volcanic areas. Possible explanations include complex rupture geometries and tensile earthquakes. Tensile earthquakes occur by opening or closure of cracks during rupturing. They are likely to be often connected with fluids that cause pressure changes in the pore space of rocks leading to earthquake triggering. Tensile components have been reported for swarm earthquakes in West Bohemia in 2000. The aim and subject of this work is an assessment and the accurate determination of such tensile components for earthquakes in anisotropic media. Currently used standard techniques for the retrieval of earthquake source mechanisms assume isotropic rock properties. By means of moment tensors, equivalent forces acting at the source are used to explain the radiated wavefield. Conversely, seismic anisotropy, i.e. directional dependence of elastic properties, has been observed in the earth's crust and mantle such as in West Bohemia. In comparison to isotropy, anisotropy causes modifications in wave amplitudes and shear-wave splitting. In this work, effects of seismic anisotropy on true or apparent tensile source components of earthquakes are investigated. In addition, earthquake source parameters are determined considering anisotropy. It is shown that moment tensors and radiation patterns due to shear sources in anisotropic media may be similar to those of tensile sources in isotropic media. In contrast, similarities between tensile earthquakes in anisotropic rocks and shear sources in isotropic media may exist. As a consequence, the interpretation of tensile source components is ambiguous. The effects that are due to anisotropy depend on the orientation of the earthquake source and the degree of anisotropy. The moment of an earthquake is also influenced by anisotropy. The orientation of fault planes can be reliably determined even if isotropy instead of anisotropy is assumed and if the spectra of the compressional waves are used. Greater difficulties may arise when the spectra of split shear waves are additionally included. Retrieved moment tensors show systematic artefacts. Observed tensile source components determined for events in West Bohemia in 1997 can only partly be attributed to the effects of moderate anisotropy. Furthermore, moment tensors determined earlier for earthquakes induced at the German Continental Deep Drilling Program (KTB), Bavaria, were reinterpreted under assumptions of anisotropic rock properties near the borehole. The events can be consistently identified as shear sources, although their moment tensors comprise tensile components that are considered to be apparent. These results emphasise the necessity to consider anisotropy to uniquely determine tensile source parameters. Therefore, a new inversion algorithm has been developed, tested, and successfully applied to 112 earthquakes that occurred during the most recent intense swarm episode in West Bohemia in 2000 at the German-Czech border. Their source mechanisms have been retrieved using isotropic and anisotropic velocity models. Determined local magnitudes are in the range between 1.6 and 3.2. Fault-plane solutions are similar to each other and characterised by left-lateral faulting on steeply dipping, roughly North-South oriented rupture planes. Their dip angles decrease above a depth of about 8.4km. Tensile source components indicating positive volume changes are found for more than 60\% of the considered earthquakes. Their size depends on source time and location. They are significant at the beginning of the swarm and at depths below 8.4km but they decrease in importance later in the course of the swarm. Determined principle stress axes include P axes striking Northeast and Taxes striking Southeast. They resemble those found earlier in Central Europe. However, depth-dependence in plunge is observed. Plunge angles of the P axes decrease gradually from 50° towards shallow angles with increasing depth. In contrast, the plunge angles of the T axes change rapidly from about 8° above a depth of 8.4km to 21° below this depth. By this thesis, spatial and temporal variations in tensile source components and stress conditions have been reported for the first time for swarm earthquakes in West Bohemia in 2000. They also persist, when anisotropy is assumed and can be explained by intrusion of fluids into the opened cracks during tensile faulting.},
  subject      = {Seismologie},
  language  = {en}
}
@misc{Petersen2017,
  type      = {Master Thesis},
  author    = {Petersen, Gesa Maria},
  title     = {Source array and receiver array analysis of Vogtland/ West Bohemia earthquake clusters},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406671},
  school      = {Universit{\"a}t Potsdam},
  pages     = {107},
  year      = {2017},
  abstract  = {Die Region Vogtland/ West B{\"o}hmen im Grenzgebiet zwischen Deutschland und Tschechien ist bekannt f{\"u}r ihre geologische Aktivit{\"a}t. Holoz{\"a}ner Vulkanismus, Gasaustritte an Mofetten und Quellen und wiederkehrende Erdbebenschw{\"a}rme sind Ausdruck geodynamischer Prozesse im Untergrund. W{\"a}hrend des Erdbebenschwarms 2008/2009 in Nov{\´y} Kostel installierte die Universit{\"a}t Potsdam ein tempor{\"a}res Array in Rohrbach, in einer Epizentraldistanz von etwa 10 km und mit einer Aperatur von etwa 0.75 km. 22 Erdbeben wurden f{\"u}r Quellarray- beam forming ausgew{\"a}hlt. Quellarrays sind {\"o}rtliche Cluster von Erdbeben, die von einer Empf{\"a}ngerstation aufgezeichnet werden. Wegen der Reziprozit{\"a}t der Green'schen Funktionen k{\"o}nnen diese in {\"a}hnlicher Weise genutzt werden wie Empf{\"a}ngerarrays, bei denen mehrere Stationen ein einzelnes Beben aufzeichnen. Die Kreuzkorrelationskoeffizienten aller Beben des Quellarrays, aufgezeichnet an einer einzelnen Station, sind in der Regel h{\"o}her als f{\"u}r einzelne Ereignisse, die an allen Stationen des Empf{\"a}ngerarrays aufgezeichnet wurden. Dies deutet hinsichtlich der aufgel{\"o}sten Frequenzen auf einen heterogenen Untergrund unter den Array-Stationen und ein vergleichsweise homogenes Quellarray-Volumen hin. Beam forming wurde mit den horizontalen und vertikalen Spuren aller Quellarray-Beben, aufgezeichnet auf allen 11 Stationen des Empf{\"a}ngerarrays, durchgef{\"u}hrt. Die Ergebnisse wurden im Hinblick auf Konversionen und reflektierte Phasen analysiert. W{\"a}hrend die theoretische Richtung der direkten P-Welle im Falle der Quellarray-Aufzeichnungen gut {\"u}bereinstimmt, wird eine Empf{\"a}ngerarray-Missweisung von 15° bis 25° beobachtet. Eine PS Phase, die der direkten P Phase folgt und eine m{\"o}gliche SP Phase, die kurz vor der direkten S-Phase ankommt, wurden auf den summierten Spuren mehrerer Stationen interpretiert. Aus der Betrachtung der Laufzeiten resultiert eine Konversionstiefe von 0.6-0.9 km Tiefe. Ein zweites Quellarray, bestehend aus 12 tieferen Beben wurde zus{\"a}tzlich analysiert, um eine nach ca. 0.85 s ausschließlich auf den Aufzeichnungen tieferer Beben auftretende Strukturphase zu deuten. Zus{\"a}tzlich zum beam forming wurden zwei Lokalisierungsmethoden von Reflexionen und Konversionen f{\"u}r einfach reflektierte/konvertierte Phasen entwickelt und zur Auswertung verwendet. W{\"a}hrend die erste, analytische Methode eine homogene Geschwindigkeit entlang des Laufwegs annimmt, wird in der zweiten Methode eine 3-D-Rastersuche ausgef{\"u}hrt, in der ein 1-D-Geschwindigkeitsmodell verwendet wird. Auf Grund der eindeutigen beam forming Ergebnisse und der hohen {\"A}hnlichkeit der Wellenformen der Erdbeben, die f{\"u}r das Quellarray genutzt wurden, bieten Quellarrays bestehend aus Mikrobeben aus dem untersuchten Gebiet gute M{\"o}glichkeiten zur Untersuchung von Krustenstrukturen.},
  language  = {en}
}
@article{HiemerRoesslerScherbaum2012,
  author    = {Hiemer, Stefan and R{\"o}ßler, Dirk and Scherbaum, Frank},
  title     = {Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array},
  series = {Journal of seismology},
  volume    = {16},
  journal   = {Journal of seismology},
  number    = {2},
  publisher = {Springer},
  address   = {Dordrecht},
  issn      = {1383-4649},
  doi       = {10.1007/s10950-011-9256-5},
  pages     = {169 -- 182},
  year      = {2012},
  abstract  = {The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M (L) < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between 19 October 2008 and 18 March 2009 with magnitudes in the range of -aEuro parts per thousand 1.2 a parts per thousand currency signaEuro parts per thousand M (L) a parts per thousand currency signaEuro parts per thousand 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M (c) = -aEuro parts per thousand 0.4, when compared to the regional networks operating in West Bohemia (M (c) > 0.0). In the course of this work, the main temporal features (frequency-magnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times) suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in our studied swarm period after 19 October, the b value of the Gutenberg-Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior of the seismic moment release. The corresponding total seismic moment release of 1.02x10(17) Nm is equivalent to M (L,max) = 5.4.},
  language  = {en}
}