On the relation of stress and deformation fields to natural and induced seismicity [Elektronische Ressource] / Geoforschungszentrum Potsdam, Stiftung des Öffentlichen Rechts. Vorgelegt von Marco Bohnhoff

Bohnhoff

Informations

• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2006
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Scientific Technical Report STR 06/04 GeoForschungsZentrum Potsdam



























ISSN 1610-0956 Scientific Technical Report STR 06/04 GeoForschungsZentrum Potsdam








On the relation of stress and deformation fields to natural
and induced seismicity






Habilitationsschrift
zur Erlangung der venia legendi
der Fakultät für Geowissenschaften
der Ruhr-Universität Bochum







vorgelegt von




Dr. Marco Bohnhoff




aus Hameln



Juni 2005







Scientific Technical Report STR 06/04 GeoForschungsZentrum Potsdam



















































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Contents:




Chapter Title Page


1. Overiew 5
2. Probing the crust to 9 km depth: fluid injection experiments 17
and induced seismicity at the KTB superdeep drilling hole,
Germany.
Reference: Baisch et al., Bull. Seism. Soc. Am., 92(6), 2369-2380, 2002.

3. Mutual relationship between microseismicity and seismic 37
reflectivity: Case study at the German Continental Deep
Drilling Site (KTB).
Reference: Rothert et al., GRL, 30(17), 1893, 2003.

4. Fault mechanisms of fluid-injection induced seismicity and 47
their relation to local fault structure and stress field
Reference: Bohnhoff et al., J. Geophys. Res., 109, B02309, 2004.

5. Strain Partitioning and Stress Rotation at the North Anato- 67
lian Fault Zone from aftershock focal mechanisms of the 1999
Izmit Mw=7.4 Earthquake
Reference: Bohnhoff et al., Geophys. J., Int.,2005, submitted.

6. Deformation and Stress regimes in the forearc of the Hellenic 87
subduction zone from inversion of focal mechanisms
Reference: Bohnhoff et al., J. Seismol.,2005, accepted.

7. CYCNET: A temporary seismic network on the Cyclades 115
(Aegean Sea, Greece)
Reference: Bohnhoff et al., Seismol. Res. Lett., 75(3), 352-357, 2004.

8. Microseismic activity in the Hellenic Volcanic Arc, Greece, 127
with emphasis on the seismotectonic setting of the Santorini-
Amorgos zone
Reference: Bohnhoff et al., Tectonophysics, 2005, submitted.

9. Indications for a balanced state of the upper plate in the 147
central magmatic arc, Greece, from spatial distribution
of microseismic activity
Reference: Bohnhoff et al., Geophys. Res. Lett.,2005, to be submitted.




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1. Overview

Global seismic networks are now in operation for about one century and their recordings
contributed significantly to the present understanding of ongoing deformation of the Earth. It
was only during the past 2-3 decades that a remarkable step forward was realized through
regional network densification and use of advanced data-acquisition technology that permitted
to record high-quality digital broadband data on a global scale. Simultaneously, new
developments in data evaluation techniques allowed moving from purely kinematical analysis
towards sophisticated dynamic interpretations of the acquired data.
The global magnitude detection threshold for earthquakes is in the order of M=4. However,
today this threshold remains mainly for offshore regions (especially large-scaled Deep-Sea
Basins), less developed regions (e.g. most of the African continent) and inaccessible parts of
the world (e.g. Polar Regions). An immense densification of seismic stations was achieved in
a number of regions such as California, Japan or Western Europe resulting in decreased
regional thresholds in the order of M=2. In recent years, the subsequently growing data base
of high-quality recordings from regional permanent seismic networks permitted to refine
earlier initial seismotectonic models pioneered in the 1970s. However, in many cases they
still form the backbone for state of the art descriptions.
In order to generate seismotectonic models for selected regions today, both is needed: high-
quality recordings from appropriate local seismic networks as well as reliable long-term based
information on the regional tectonic setting. In this respect, the World Stress Map Project
(WSM, Heidbach et al., 2004; Reinecker et al., 2004) offers a fundamental data base on stress
field orientation worldwide. The WSM data base contains more than 13600 quality ranked
data sets and data is freely available from their website. To determine the tectonic stress
orientation different types of stress indicators are used in the WSM. They are grouped into
four categories which are (1) earthquake focal mechanisms, (2) well bore breakouts and
drilling induced fractures, (3) in-situ stress measurements and (4) young geologic data. A
detailed description of the different methodologies used to derive stress information from
these indicators can be found in Sperner et al. (2003), Zoback and Zoback (1991) and Zoback
et al. (1989).
As in-situ measurements of stress field orientation and stress magnitude are necessarily
associated with the presence of boreholes they are extremely cost-intensive. Furthermore,
with regard to the determination of stress field orientation from fault plane solutions it has to
be noted that there is an inherent error in all stress orientations derived from single focal
mechanism solutions (McKenzie, 1969). Taking into consideration recent developments in
seismic data acquisition technology, dense local networks offer the outstanding opportunity to
significantly refine the stress maps on local scale. Different methods have been developed to
determine the orientations of the three principal stresses, σ , as well as a relative stress 1-3
magnitude R defined as R=( σ –σ )/( σ – σ ) reflecting the shape of the stress ellipsoid from 2 3 1 3
focal mechanism data. The two most common approaches of stress tensor inversion were
introduced by Gephart and Forsyth (1984) and Michael (1987). The methods themselves are
described in more detail in the relevant chapters of this work. Here, emphasis should be given
on the accuracy of the stress field as determined by the stress tensor inversion. Fault
mechanisms serve as input data. Assuming the focal mechanisms were determined from
appropriate networks with sufficient station distribution to achieve a good coverage of the
focal sphere, their accuracy can realistically be estimated to 5° at best. As a consequence, the
accuracy in orientation of the principal stresses can neither be better. Once stress tensor
inversion is applied to the data, the results can be related to the regional long-term stress field
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(WSM) and used to evaluate the local stress field orientation with respect to possible
variations in space and time.

This work describes the results of seismological field campaigns and experiments using
combined seismic networks of varying geometries such as a combined seismic downhole and
surface network or a combined temporary local and permanent regional network. The
networks were deployed in different tectonic environments, i.e. in a stable intraplate
surrounding, at a plate boundary along a major transform fault zone and in forearc and
backarc settings of a subduction zone to record different types of seismicity (induced
earthquakes, aftershocks, subduction-related seismicity). Recording periods are typically
several months. The basic ideas behind all the different experiments and studies presented
here can be described as follows: In a first step, a state of the art seismic network is designed
and deployed in a selected area to record local (micro)seismic activity at low magnitude
detection threshold. The acquired data base is then evaluated using standard processing
techniques to generate a proper hypocenter catalog for the area of investigation during the
observational pe