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Titel |
Application of a time probabilistic approach to seismic landslide hazard estimates in Iran |
VerfasserIn |
A. M. Rajabi, V. Del Gaudio, D. Capolongo, M. Khamehchiyan, M. R. Mahdavifar |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250031367
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Zusammenfassung |
Iran is a country located in a tectonic active belt and is prone to earthquake and
related phenomena. In the recent years, several earthquakes caused many fatalities
and damages to facilities, e.g. the Manjil (1990), Avaj (2002), Bam (2003) and
Firuzabad-e-Kojur (2004) earthquakes. These earthquakes generated many landslides.
For instance, catastrophic landslides triggered by the Manjil Earthquake (Ms =
7.7) in 1990 buried the village of Fatalak, killed more than 130 peoples and cut
many important road and other lifelines, resulting in major economic disruption.
In general, earthquakes in Iran have been concentrated in two major zones with
different seismicity characteristics: one is the region of Alborz and Central Iran and
the other is the Zagros Orogenic Belt. Understanding where seismically induced
landslides are most likely to occur is crucial in reducing property damage and loss
of life in future earthquakes. For this purpose a time probabilistic approach for
earthquake-induced landslide hazard at regional scale, proposed by Del Gaudio et al. (2003),
has been applied to the whole Iranian territory to provide the basis of hazard estimates.
This method consists in evaluating the recurrence of seismically induced slope
failure conditions inferred from the Newmark’s model. First, by adopting Arias
Intensity to quantify seismic shaking and using different Arias attenuation relations for
Alborz - Central Iran and Zagros regions, well-established methods of seismic
hazard assessment, based on the Cornell (1968) method, were employed to obtain the
occurrence probabilities for different levels of seismic shaking in a time interval of
interest (50 year). Then, following Jibson (1998), empirical formulae specifically
developed for Alborz - Central Iran and Zagros, were used to represent, according to the
Newmark’s model, the relation linking Newmark’s displacement Dn to Arias intensity Ia
and to slope critical acceleration ac. These formulae were employed to evaluate
the slope critical acceleration (Ac)x for which a prefixed probability exists that
seismic shaking would result in a Dn value equal to a threshold x whose exceedence
would cause landslide triggering. The obtained ac values represent the minimum
slope resistance required to keep the probability of seismic-landslide triggering
within the prefixed value. In particular we calculated the spatial distribution of
(Ac)x for x thresholds of 10 and 2 cm in order to represent triggering conditions for
coherent slides (e.g., slumps, block slides, slow earth flows) and disrupted slides
(e.g., rock falls, rock slides, rock avalanches), respectively. Then we produced a
probabilistic national map that shows the spatial distribution of (Ac)10 and (Ac)2, for a
10% probability of exceedence in 50 year, which is a significant level of hazard
equal to that commonly used for building codes. The spatial distribution of the
calculated (Ac)xvalues can be compared with the in situ actual ac values of specific
slopes to estimate whether these slopes have a significant probability of failing under
seismic action in the future. As example of possible application of this kind of
time probabilistic map to hazard estimates, we compared the values obtained for
the Manjil region with a GIS map providing spatial distribution of estimated ac
values in the same region. The spatial distribution of slopes characterized by ac <
(Ac)10 was then compared with the spatial distribution of the major landslides
of coherent type triggered by the Manjil earthquake. This comparison provides
indications on potential, problems and limits of the experimented approach for the study
area.
References
Cornell, C.A., 1968: Engineering seismic risk analysis, Bull. Seism. Soc. Am., 58,
1583-1606.
Del Gaudio V., Wasowski J., & Pierri P., 2003: An approach to time probabilistic
evaluation of seismically-induced landslide hazard. Bull Seism. Soc. Am., 93, 557-569.
Jibson, R.W., E.L. Harp and J.A. Michael, 1998: A method for producing digital
probabilistic seismic landslide hazard maps: an example from the Los Angeles, California,
area, U.S. Geological Survey Open-File Report 98-113, Golden, Colorado, 17 pp. |
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