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A new seismological network for Bavaria and its application to the study of meteorologically triggered earthquake swarms

Kraft, T. (2006), A new seismological network for Bavaria and its application to the study of meteorologically triggered earthquake swarms, LMU Munich, Faculty of Geosciences.

This thesis addresses to self-contained topics and is therefore structured in tow parts. The first part describes the installation of a new seismological network for Bavaria, whereas the second part focuses on the investigation of rainfall induced seismicity near Bad Reichenhall in southeastern Bavaria.

Part 1

Because of the focus of the existing seismological stations on teleseismic and regional events, the capability of locating local earthquakes in various regions of Bavaria was quite limited. To overcome this situation 15 new stations were installed in the country. Additionally, six existing stations were updated to state-of-the-art technology in a second stage. The network geometry closely oriented on the seismicity of Bavaria, with densly spaced stations in areas were activity is high and promising scientific problems could be addressed. The software concept was, as far as possible, adopted from the GEOFON Project of th GeoFoschungsZentrum Potsdam (GFZ), which is already used for the German Regional Seismic Network (GRSN) and other European networks. This assures an easy data transfer with other services and allows the future incorporation of real-time data of the Bavarian network in an European and global seismological networks.

Part 2

In the second part of this thesis, the focus will be laid on one of the dense sub-networks in southeastern Bavaria. Here, near the town of Bad Reichenhall, a connection between rainfall and seismicity is suggested since the early 1970ties. However, because of the lack of continuous high-quality data such a correlation could never be tested by means of a physical model. In three papers the observation of above average rainfall in 2002 and associated earthquake swarms are studied in detail. Starting with an overview paper with first location results and interpretation in Chapter 3, the discussion of cluster analysis, high-precision relocation and focal-mechanism analysis in Chapter 4, and finally by statistical modeling of the relocated seismicity by means of point process modeling and pore-pressure diffusion assuming a rate-state earthquake friction model in Chapter 5.

Although, seasonal variability of seismicity related to ground water recharge and precipitation has been previously observed on regional scales, a statistically significant causal relationship between rainfall and earthquake activity for an isolated region can be shown here for the first time. The analysis of the high quality meteorological and seismic data in the Mt. Hochstaufen region yields clear evidence that tiny pore pressure changes induced by rainfall are able to trigger earthquake activity even at 4 km depth via the mechanism of fluid diffusion. Stress changes of the order of 5-13 mbar are found to trigger earthquakes. This is much less than usually produced in fluid injection experiments (several 100 bars and more), indicating an extreme sensitivity of the crust with regard to tiny changes. This might be an universal feature which can, however, only be seen in the rare occasion of an isolated but critical system, like the study area.

Although, the derived focal mechanisms indicate an influence of the Saalach Fault Zone on the stress regime of the study area, the reason for the criticality of the seismogenic volume in the Mt. Hochstaufen region is not yet finally resolved. However, the high correlation between rainfall-induced pressure changes at depth and seismicity opens the possibility of forecasting future earthquake rates on the basis of rainfall data in this region. Regarding the small volume in which the earthquakes take place, the almost yearly occurring earthquake swarms and the permanent, seismo-meteorological monitoring network, Mt. Hochstaufen provides nearly controlled experimental conditions to study fluid-induced seismicity and the physics of earthquake swarms.
Further information
  author = {T. Kraft},
  month = {aug},
  school = {LMU Munich, Faculty of Geosciences},
  title = {{A new seismological network for Bavaria and its application to the study of meteorologically triggered earthquake swarms}},
  year = {2006},
  language = {en},
  url = {http://edoc.ub.uni-muenchen.de/archive/00005857/},
%0 Thesis
%A Kraft, T.
%D 2006
%T A new seismological network for Bavaria and its application to the study of meteorologically triggered earthquake swarms
%U http://edoc.ub.uni-muenchen.de/archive/00005857/
%8 aug
%I LMU Munich, Faculty of Geosciences
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