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| Titel |
A new fault-thermometer based on vitrinite maturation by coseismic frictional heating |
| VerfasserIn |
Manami Kitamura, Hideki Mukoyoshi, Takehiro Hirose |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094159
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| Publikation (Nr.) |
 EGU/EGU2014-9552.pdf |
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| Zusammenfassung |
| To detect frictional heating effects along faults provides key insight into the dynamics of
earthquakes and faulting [e.g., Brodsky et al., 2010]. Evidence of substantial frictional
heating along a fault is also a reliable indicator determining whether a fault has slipped at
high velocity in the past, which is crucial for assessing earthquake and tsunami hazard.
The reflectance (R) measurement of vitrinite, one of the primary components of
coals, has been considered a possible thermometer of fault zones, especially in
accretionary wedges where vitrinite fragments are common [e.g., Sakaguchi et
al., 2011]. Under normal burial conditions, vitrinite reflectance (R) increases by
irreversible maturation reaction as temperature is elevated and thus sensitively records the
maximum temperature to which the vitrinite is subjected. However, the commonly
used kinetic models of vitrinite maturation [e.g., Sweeney and Burnham, 1990]
may not yield accurate estimates of the peak temperature in a fault zone resulting
from fast frictional heating rates [Kitamura et al., 2012; Fulton and Harris, 2012].
Thus, we performed high-velocity friction experiments aimed at revealing coal
maturation by frictional heat generated at slip velocities representative of natural
earthquakes up to 1.3 m/s. Our experimental results indicate that coal can mature in
typical earthquake rise time (e.g., ~10 seconds) and R increases exponentially with
increasing peak temperature [Kitamura et al., 2012]. In addition to these results, we will
present the effects of water, atmosphere condition (oxygenic/anoxic), and initial
R value and grain size of coal on coal maturation during coseismic faulting, and
eventually propose a new fault-thermometer based on coal maturation by rapid frictional
heating.
Using the correlation between R and temperature rises we estimate the dynamic friction
during coseismic faulting in the shallow portions of a megasplay fault in the Nankai trough.
The fault zone has a ~20 mm thickness of shear localized zone. An average R of vitrinite
grains in host rocks is ~0.24% which corresponds to a maximum burial temperature of about
0.80%. Although
Sakaguchi et al. (2011) reported ~390oC using a kinetic model of Sweeney and
Burnham (1990), the high R corresponds to ~150oC using our new thermometer.
This temperature anomaly can be explained by dynamic shear stress of 0.53 MPa
(dynamic friction of ~0.18), assuming fault displacement of 15 m at the current depth
conditions. These results are consistent with the estimate of dynamic friction from
temperature measurement across the fault zone after the 1999 Chi-Chi, Taiwan
earthquake [e.g., Kano et al., 2006] and with the result of high-velocity friction
experiments [e.g., Di Toro et al., 2011]. The fault-thermometer based on vitrinite
maturation can be a possible tool to estimate of fault parameters from natural fault zones. |
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