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| Titel |
Fault Specific Seismic Hazard Maps as Input to Loss Reserves Calculation for Attica Buildings |
| VerfasserIn |
Georgios Deligiannakis, Ioannis Papanikolaou, Alexandros Zimbidis, Gerald Roberts |
| 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 |
250093713
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| Publikation (Nr.) |
 EGU/EGU2014-8700.pdf |
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| Zusammenfassung |
| Greece is prone to various natural disasters, such as wildfires, floods, landslides and
earthquakes, due to the special environmental and geological conditions dominating in
tectonic plate boundaries. Seismic is the predominant risk, in terms of damages and casualties
in the Greek territory. The historical record of earthquakes in Greece has been published from
various researchers, providing useful data in seismic hazard assessment of Greece. However,
the completeness of the historical record in Greece, despite being one of the longest
worldwide, reaches only 500 years for M ≥ 7.3 and less than 200 years for M ≥ 6.5.
Considering that active faults in the area have recurrence intervals of a few hundred to several
thousands of years, it is clear that many active faults have not been activated during
the completeness period covered by the historical records. New Seismic Hazard
Assessment methodologies tend to follow fault specific approaches where seismic
sources are geologically constrained active faults, in order to address problems
related to the historical records incompleteness, obtain higher spatial resolution and
calculate realistic source locality distances, since seismic sources are very accurately
located. Fault specific approaches provide quantitative assessments as they measure
fault slip rates from geological data, providing a more reliable estimate of seismic
hazard.
We used a fault specific seismic hazard assessment approach for the region of Attica. The
method of seismic hazard mapping from geological fault throw-rate data combined three
major factors:
Empirical data which combine fault rupture lengths, earthquake magnitudes and
coseismic slip relationships.
The radiuses of VI, VII, VIII and IX isoseismals on the Modified Mercalli (MM)
intensity scale.
Attenuation - amplification functions for seismic shaking on bedrock compared
to basin filling sediments.
We explicitly modeled 22 active faults that could affect the region of Attica, including Athens,
using detailed data derived from published papers, neotectonic maps and fieldwork
observations. Moreover, we incorporated background seismicity models from the historic
record and also the subduction zone earthquakes distribution, for the integration of strong
deep earthquakes that could also affect Attica region.
We created 4 high spatial resolution seismic hazard maps for the region of Attica, one for
each of the intensities VII – X (MM). These maps offer a locality specific shaking recurrence
record, which represents the long-term shaking record in a more complete way,
since they incorporate several seismic cycles of the active faults that could affect
Attica. Each one of these high resolution seismic hazard maps displays both the
spatial distribution and the recurrence, over a specific time period, of the relevant
intensity.
Time – independent probabilities were extracted based on these average recurrence
intervals, using the stationary Poisson model P = 1 -e-λt. The “λ” value was provided by
the intensities recurrence, as displayed in the seismic hazard maps. However, the insurance
contracts usually lack of detailed spatial information and they refer to Postal Codes level,
akin to CRESTA zones. To this end, a time-independent probability of shaking at intensities
VII - X was calculated for every Postal Code, for a given time period, using the Poisson
model.
The reserves calculation on buildings portfolio combines the probability of events of
specific intensities within the Postal Codes, with the buildings characteristics, such as the
building construction type and the insured value. We propose a standard approach for the
reserves calculation K(t) for a specific time period:
K (t) = x2 -
[x1 -
y1 -
P1(t) + x1 -
y2 -
P2(t) + x1 -
y3 -
P3(t) + x1 -
y4 -
P4(t)]
x1
which is a function of the probabilities of occurrence for the seismic intensities VII – X
(P1(t) -P4(t)) for the same period, the value of the building x1, the insured value x2 and the
characteristics of the building, such as the construction type, age, height and use of property
(y1 - y4).
Furthermore a stochastic approach is also adopted in order to obtain the relevant
reserve value K(t) for the specific time period. This calculation considers a set of
simulations from the Poisson random variable and then taking the respective expectations. |
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