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Project 3: Seismic
Hazard, Risk and Loss
Project Manager: Hilmar Bungum (NORSAR)
The project is engaged in
research topics within the following fields:
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Quantification of earthquake hazard (exceedance
probability of a certain ground shaking amplitude/level) including
the influence of soil amplification characteristics
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Seismic vulnerability of the built and populated environment
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Development of models and software tools for risk quantification (risk
= vulnerability ∙ hazard)
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Loss modeling at different scales
Here, the term earthquake hazard refers to the occurrence probabilities
of damaging ground motions, exclusively relating to natural phenomena
and processes, while risk and loss results from combining the earthquake
hazard with the vulnerability of the building stock.
Figure 1. Collapse of a dwelling due to the Kashmir earthquake of
October 8, 2005.
1
Introduction
Earthquakes hit
without warning (Fig. 1), but with a damage potential that is generally
confined to a limited area around the epicentre or along the fault
trace. In most cases, it is the combination of earthquake magnitude,
poor building quality, and high population density of the area of
highest shaking that cause the disasters. This is one of the reasons
why, with increasing population and urbanization in earthquake-prone
countries, the losses from earthquakes have been increasing
significantly over the last decades (Fig. 2). When comparing earthquake
risk with other natural risks it is informative to see from Fig. 2 that,
at low probabilities, the earthquake risk is far above the risk from
other natural hazards (even in low-seismicity regions like e.g.,
Germany).
This implies that the
earthquake damage increases strongly with decreasing occurrence
probabilities (increasing return periods), which in turn means that the
largest ones are rare but very destructive. This indicates that at any
given location one cannot rely on ‘human lifetime memory’ as a basis for
precautionary measures: science is needed instead.
At present,
earthquakes cannot be predicted within reasonable time and spatial
windows, and the viable disaster prevention is therefore to delineate
the earthquake-prone areas and to understand in detail the factors that
turn an earthquake into a disaster or prevents the same.
Only with such
knowledge, society can develop the capacity to limit future tragedies,
and mitigation is a key word for the work within the ICG Project 3.
Figure 2. (left)
Global economic losses per decade in billions of US-$, normalized to the
year 2000 value (Munich Re) and (right) risk curves due to storms,
floods, and earthquakes for the city of Cologne, Germany. The data
considers losses at buildings and in the sectors private housing,
commerce, and industry for the year 2000 (courtesy of G. Grünthal,
2004).
2
Research topics
Earthquake disasters
are of course caused by the combination of strong ground shaking and
buildings having low structural capacity, thus showing a poor
performance during earthquake action and being unable to withstand the
shaking without damages. Two main factors that therefore can turn an
earthquake into a disaster are the vulnerability of (inadequately
constructed) buildings, and unfavorable soil conditions beneath the
building. The latter will amplify ground shaking effects and in some
cases even contribute to liquefaction or sliding. The earthquakes in
Mexico City 1985 and Armenia 1988 are prime examples of the importance
of these two factors.
Many of the fast
growing cities today are located on old lake beds and land fills with
strong soil amplification potentials. The shaking contribution of these
factors are important research targets in ICG Project 3, and Fig. 3
attempts to synthesize the overall earthquake vulnerability problem and
some of the topics that are addressed in this project.
Figure 3. Sketch of
some of the topics (inside the hatched circle) that are addressed in
this project, while the neighboring research areas (outside the circle)
are covered only more briefly.
2.1
Earthquake hazard and site amplification
NORSAR has been
dealing with earthquake hazard-related problems for more than 30 years,
both on the research side and as a partner for the construction
industry. The efforts have partly been within earthquake hazard
methodology, in particular probabilistic methods, but also to develop
the underlying knowledge needed to perform sufficiently reliable
analyses, concentrating on the following topics:
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earthquake hazard methodologies
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seismotectonics and earthquake source models
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ground-motion models (wave attenuation)
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site response (soil amplification)
Since the first two of
these topics have been thoroughly covered in earlier works, the efforts
within ICG Project 3 have been focused to some extent on the third topic
but even more on the last one, as it will be shown in the subsequent
sections. Fig. 4 illustrates some results from a study aimed at
developing criteria for selecting and adjusting ground-motion models for
specific target regions. It can be seen that the effect on the spectrum
of the near-surface geology may be considerable, demonstrating the
importance of detailed soil response and site characterization efforts.
Below, a more detailed description of such investigations is presented.
Figure 4. VS30
(average shear-wave velocity of the soil in the uppermost 30 m)
adjustment factors using ‘generic’ rock models and VS30 and kappa
(near-surface attenuation) adjustment factors. The coloured lines
represent different ground motion (host) relations and the target kappa
value is equal to 0.0125 s.
2.2 Seismic
risk and loss analysis software (SELENA)
The single most
comprehensive work towards earthquake risk calculation until today is
condensed in HAZUS, a software system which was prepared by the Federal
Emergency Management Agency (FEMA) for use in the United States. The
basic approach behind this software is physical-analytical (and hybrid),
and large resources had been used to define both capacity and fragility
(vulnerability) curves for different building types and levels of design
categories. From an engineering perspective this analytical approach is
very attractive, however, it quickly becomes complex even for simple
buildings, and a calibration to the damage records of historical
earthquake events is necessary. Since HAZUS previously was an
‘inaccessible’ software, NORSAR has developed a comparable stand-alone
software that can be applied anywhere in the world, and which includes a
logic tree-based weighting of input parameters that allows for the
computation of confidence intervals. The open-source software package is
called SELENA – Seismic Loss Estimation using a Logic Tree Approach.
Much of NORSARs recent
work was concerned with the development of SELENA, which in turn
establishes the basis for new research initiatives and applied projects.
Since January 2007, SELENA is offered as open source software, available
for download at
http://www.norsar.no/seismology/selena.html, which we hope will
attract the interest from new users. The SELENA software will now also
be more widely used and distributed through research collaboration
programs with India, Central America, and within different EU projects.
The SELENA/HAZUS
approach is based on the ‘capacity-spectrum method’ since it combines
the ground-motion input in terms of a response spectrum (spectral
acceleration versus spectral displacement) with the building’s specific
capacity curve. The philosophy behind this is that any building is
structurally damaged by its permanent horizontal displacement (and not
by the acceleration itself). For each building and building type the
inter-story drift (relative drift of the stories within a multi-story
building) is a function of the applied lateral force that can be
analytically determined and transformed into building capacity curves
(capacity to withstand accelerations without permanent displacements).
Building capacity curves naturally vary between different building
types, and also between different regions, reflecting on building code
regulations and local construction practice.
Figure 5. The
principles of analytical risk assessment approaches (e.g. SELENA) are
based on the crossover of physical capacity curves representing the
nonlinear lateral displacement behaviour of the structure and the damped
ground-motion displacement spectrum (top). Once the performance point is
assigned damage probabilities for the five different damage states can
be derived from the fragility curves (bottom).
2.3
Vulnerability
Within the preparation
of HAZUS, FEMA developed capacity curves for 36 building types (being
representative for the United States) in four earthquake load regimes
(reflecting the variation in building regulations as a function of time
across the United States). These 144 capacity curves were analytically
developed, but are adjusted so that empirical knowledge is incorporated
in the curves whenever possible. The building capacity curve is
described by three control points representing design, yield and
ultimate capacity. Up to the yield point, the building’s capacity curve
is assumed to behave linearly (ideal elastic). From the yield point to
the ultimate point, the capacity curve changes from an ideal elastic to
a fully plastic state (curved form), and the curve is assumed to remain
fully plastic past the ultimate point (linear form). A bilinear
representation (two linear parts) is sometimes used to simplify the
model. The vulnerability curves (also called fragility curves) are
developed as lognormal probability distributions of damage from the
capacity curves.
Using inventory data
from Oslo (Norway) with 902 reinforced-concrete (RC) buildings from the
district Grünerløkka, a simple classification of the buildings yields
fragility curves as shown in Fig. 6, for Damage Limit States 1 to 3 (1:
no damage, 2: slight damage, and 3: moderate damage).
Figure 6. Fragility
curves for 902 reinforced-concrete buildings (1- to 3-story) in Oslo for
Damage Limit States 1, 2, and 3 using a displacement-based approach.
2.4 Damage and
loss estimation
Currently, SELENA
computes seismic losses using the capacity spectrum method. The losses
are computed as aggregates of the inflicted damages to each building
type within a predefined area (a city quadrant, census tract or any
user-specified area). The damage to the physical environment can then be
converted to monetary damages as well as to estimates of casualties
using empirical relations. The damages are presented in tabular form and
any appropriate mapping or graphing software can be used to display the
results in easy understandable figures.
2.5
Illustration of risk and loss results – RISe
One of the advantages
of SELENA is its portability between platforms and its independence of
graphic software. This independence can also be a disadvantage, however,
if the potential user groups feel the lack of graphical interface as a
deficiency.
In cooperation with
INETER, one of NORSAR’s long-term partners in Central America, a
stand-alone software tool has been developed called RISe – Risk
Illustrator foer SELENA. RISe will allow a quick and easy illustration
of the georeferenced input, inventory and output data of SELENA in
GoogleEarth (GE) and will thus substitute the use of any commercial GIS
program. Furthermore, the tool will help to demarcate the study areas in
Google Earth and to generate the SELENA input files through an
easy-to-understand and user-friendly program surface.
Different ways in
order to illustrate the inventory data or risk results are implemented
in RISe. Figures 7 and 8 shows two different ways of illustrating the
damage probabilities of a particular model building type in the case
study Oslo, Norway.
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The RISe software is
today a stand-alone software solution which substitutes the use of a
commercial GIS solution.
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It facilitates the
preparation of SELENA input files.
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It allows the
demarcation of study areas (census tracts) and illustration of
inventory data and risk results in GoogleEarth.
Figure 7. Damage
probability as illustrated by use of GoogleEarth. See legend for color
code definitions.
Figure 8. Damage
probability as illustrated by use of GoogleEarth. See legend for color
code definitions.
2.6
Tsunami modelling
Up to now, initial
seafloor displacements resulting from tsunami-triggering earthquakes are
calculated using a simple, analytical method (e.g. Okada's method;
Okada, 1992, BSSA) in most oceanographic models analysing tsunami
inundation heights at neighbouring coastlines. Although analytical
solutions are mathematically exact and inexpensive in terms of
computation powers, they only allow for very simple model geometries and
homogeneous material properties. Geist and Dmowska (1999, PAGEOPH) state
that effects of heterogeneous slip patterns on the earthquake fault
plane are important to include in the local tsunami wave field. The
amount of slip for a given seismic moment depends not only on fault
plane properties, e.g. the distribution of asperities, but also on the
shear modulus of the surrounding material, which may vary with depth in
subduction zones from 3 to 30 GPa (Bilek and Lay, 1999, Nature).
Curvature of fault plane and seafloor topography may additionally
influence the resulting displacement pattern. Such inhomogeneities can
only be captured by a numerical model.
We use the FEM
numerical method to deal with surface displacement computations
resulting from slip on a fault. GeoFEST (Jet Propulsion Laboratory at
California Institute of Technology; authors: G. Lyzenga and J. Parker)
was chosen to be the most appropriate software solution for our task,
since the code is capable to account for material inhomogeneities, a
heterogeneous slip distribution on the earthquake fault plane and
irregular fault geometry in 2-D or 3-D. Further, it is possible to
include multiple faults, seafloor topography and friction on the fault.
Figure 9.
Inhomogeneous FEM mesh used to calculate seafloor displacement resulting
from slip on earthquake faults; mesh is subdivided to represent
accretionary wedge, continental crust, oceanic plate and asthenosphere.
Figure 10. Influence
of change of subduction angle from 0° to 90°; left: vertical
displacement, right: horizontal displacement, light colour: steep
subduction angle, dark colours: shallow subduction angle.
Figure 11. Influence
of change fault plane bending; top: vertical displacement (red: bended
fault plane, black: comparison to homogeneous model), bottom: sketch of
bended fault plane.
2.7
Soil amplification studies
2.7.1 Numerical
simulation of H/V-data
The work consists of
using NGI’s Green’s functions software Laysac to simulate the
steady-state horizontal and vertical motions on ground surface due to a
distant source. The objective is then to use the simulated data to
assess the performance/validity and the range of applicability of the
H/V method for different soil profiles and especially for a range of
stiffness contrast at the rock/soil interface. The results will also be
compared with the associated transfer functions for the selected soil
profiles.
2.7.2 Instrumental soil response studies
The amplification of
seismic waves as they propagate through less consolidated sediments and
soils is, as already mentioned, a major factor behind earthquake
damages. The thick clay deposits in and around Oslo lends this region to
such studies. Although Oslo is not a place with a significant seismic
activity, a few earthquakes with noticeable intensity have occurred in
the past, including a magnitude 5.4 earthquake in the outer Oslofjord in
1904. This earthquake caused masonry building walls to crack as well as
chimneys and roof tiles to fall off the houses in the city of Oslo. The
observed significant shaking (and the associated damages) was caused by
wave amplification through the thick layers of sediments underlying
Oslo.
To investigate this
phenomenon in more detail we have conducted special studies both in 2004
and 2006, visiting 35 different sites within the city. The technique
used insisted in recording ambient seismic noise and to infer the soil
response on the basis of such data using the so-called Nakamura
technique, based on ambient noise H/V (horizontal-to-vertical) ratios.
The results (Fig. 12) are largely explaining the distribution of damages
from the 1904 earthquake.
Figure 12. Spectral
H/V ratio (median and the range of ± standard deviation) of site no. 28
(Oslo study). The peak at around 6 Hz indicates the first resonant
frequency of the soil profile.
The simple Nakamura
technique presented above is complemented by more elaborate methods
which have also been tested and used under ICG Project 3, notably an
array technique and a technique based on spectral analysis of surface
waves (SASW). The former technique has been used in a conceptual study
at Sogn Hagekoloni in Oslo, using two different array diameters. The
data have been analyzed in terms of H/V ratios on individual stations,
and a subsurface shear-wave velocity profile was established through
joint analysis of the two array geometries (Fig. 13).
Figure 13. Ambient
seismic noise recorded by two arrays with different aperture in order to
conduct non-unique forward modelling of the velocity profile that
matches the observed dispersion curves.
3
Related external projects
Several related
projects are proceeding in 2008, including the EU projects LESSLOSS,
NERIES, SAFER, and TRANSFER. In addition, MFA (UD) funded projects in
Central America, Pakistan, and India. The coordination between ICG
Project 3 and these projects will be very important in the coming years.
Within NERIES, NORSAR is charged with coordinating the development of
shake maps for Europe, and will also take part in the evaluation of risk
estimation software and loss assessments.
Within SAFER, NORSAR
is responsible for developing real time damage scenarios, where the city
of Naples and possibly Bucharest will be used as targets. Another
activity under the SAFER project is for NORSAR to develop rapid
epicentre solutions based on array data processing. NORSAR also has a
small component in TRANSFER with focus on tsunami-generating earthquake
sources in the North Atlantic.
4 Plans for 2008
- Further development
of the SELENA software with the main focus on distribution and
application
- Expansion and
adjustment of the RISe software
- Strengthening of
structural modelling and nonlinear analysis capacities
- Further work on
intra-plate ground-motion models (EU)
- Tsunami source
modelling of fault dislocations (cooperation with ICG Project 10)
- Numerical
simulation of H/V-data and further work on site amplification
- Cooperation and
coordination with other projects (EU, MFA)
- Development of
competence for multi-hazard and risk mitigation (earthquakes, tsunami,
landslides)
- Visitors program
(including students)
- Publications
(papers and reports)
5 Publications
2007-2009
5.1 Papers
with referee system
Bungum, H. (2007):
Numerical modeling of fault activities. Computers & Geosciences 33:
808–820.
Molina S. and Lindholm, C.
(2007): Estimation the confidence of earthquake damage scenarios:
examples from a logic tree approach. Journal of Seismology 11(3):
399–310.
Lang, D.H., Molina, S., and
Lindholm, C.D. (2008): Towards near-real-time damage estimation using a
CSM-based tool for seismic risk assessment. Journal of Earthquake
Engineering 12(S2),
199–210.
Prasad, J.S.R., Singh, Y.,
Kaynia, A.M., and Lindholm, C.D. (2008): Socio-Economic Clustering in
Seismic Risk Assessment of Urban Housing Stock. Earthquake Spectra,
accepted.
5.2 Other
reviewed publications
Lang, D.H., R. Merlos, L.
Holliday, and M. Lopez (2007): Vivienda de Bahareque in El Salvador.
EERI World Housing Encyclopedia. Paper #141.
Lang, D.H., O. Flores, and
L. Holliday (2007): Vivienda de adobe in Guatemala. EERI World Housing
Encyclopedia. Paper #144.
Lang, D.H., A. Amador, L.
Holliday, C. Romero, and A. Ugarte (2007): Vivienda de Minifalda in
Nicaragua. EERI World Housing Encyclopedia. Paper #148.
Rautela, P., Joshi, G.Ch.,
Singh, Y. and Lang, D.H. (2008). Koti Banal Architecture of Uttarakhand,
India. EERI World Housing Encyclopedia. Paper #150.
5.3 Papers in
proceedings
Schwarz, J., Lang, D.H.,
Abrahamczyk, L., Bolleter, W., Savary, C., Bikce, M., Genes, M.C., and
Kacin, S. (2007): Seismische Bauwerksinstrumentierung von
mehrgeschossigen Stahlbeton-bauwerken - Ein Beitrag zum SERAMAR Projekt.
D-A-CH Tagung Vienna/Austria, Sept. 2007.
Abrahamczyk, L., Schwarz,
J., Lang, D.H., Leipold, M., Genes, M.C., Bikce, M. and Kacin, S.
(2008). Building monitoring for seismic risk assessment (I):
Instrumentation of RC frame structures as a part of the SERAMAR project,
14th World Conf. on Earthq. Eng. WCEE, Beijing/China, 2008.
Schwarz, J., Lang, D.H.,
Kaufmann, C., and Ende, C. (2007): Empirical ground-motion relations for
Californian strong-motion data based on instrumental subsoil
classification. Proceedings of the Ninth Canadian Conference on
Earthquake Engineering, Ottawa, Ontario, Canada, 2007.
Schwarz, J., Langhammer,
T., Leipold, M., Abrahamczyk, Kaufmann, Ch., Lang, D.H., and Riedel, S.
(2008): Bewertung der Erdbebenverletzbarkeit eines Gebaeudebestandes in
innerstaedtischen Grossraeumen – Phase 1 des SERAMAR Projektes. D-A-CH
Mitteilungsblatt, Band 83, Sept. 2008, S2–S10.
Sigaran, C., Kaynia, A.M.,
and Hack, R. (2007). Soil stability under earthquakes: A sensitivity
analysis. 4ICEGE. June 25-28. in review.
Haugen, E.D. and Kaynia,
A.M. (2008). A comparative study of empirical models for landslide
prediction using case histories. Proc. 14th World Conf. on Earthquake
Engineering, Beijing, China, 12-17 Oct., Paper 04-02-0022.
5.4 Talks and
poster presentations
Bungum, H., Faleide, J.I.,
Pettenati, F., Schweitzer, J. and Sirovich, L. (2008). The M 5.4 October
23, 1904, Oslofjord earthquake: Reanalysis based on instrumental and
macroseismic data, 39th Nordic Seismology Seminar, Holmen Fjordhotell,
Oslo, June 2008.
Lang, D.H. and Schwarz, J.
(2007): The application of ambient seismic noise for engineering
purposes. NATO Advanced Research Workshop ‘Increasing Seismic Safety by
Combining Engineering Technologies and seismological Data’, Dubrovnik,
Croatia, September 2007 (extended abstract).
Lang, D.H., Molina, S., and
Lindholm, C.D. (2007): Towards near-real-time damage estimation using a
CSM-based tool for seismic risk assessment. International Symposium on
Earthquake Loss Estimation for Turkey (HAZTURK), September 2007,
İstanbul, Turkey.
Lang, D.H., Molina
Palacios, S., and Lindholm, C.D. (2007): The seismic risk and loss
assessment tool SELENA and its applicability for (near-)real-time damage
estimation. International workshop on seismicity and seismological
observations of the Baltic Sea region and adjacent territories,
September 10–12, 2007, Vilnius, Lithuania.
Lang, D.H., Molina, S.,
Lindholm, C.D. and Gutierrez, V. (2008). The seismic risk and loss
assessment tool SELENA – Recent developments and applications, 39th
Nordic Seismology Seminar, Holmen Fjordhotell, Oslo, June 2008.
Molina-Palacios, S.,
Galiana-Merino, J.J., Jiménez-Delgado, A., Zaragoza-Martínez, F.,
Jiménez, M.J., Gimeno-Nieves, E., Lang, D.H., and Lindholm, C.D. (2008).
Seismic risk scenarios for urban areas of Alicante Province (southeast
Spain), 14th World Conf. on Earthq. Eng. WCEE, Beijing/China, 2008.
Molina, S., Elias, C.,
Lang, D.H., Lindholm, C.D. (2008): Soil characteristics identification
of urban areas in San Salvador (El Salvador) using H/V spectral ratio
technique. 31st General Assembly of the European Seismological
Commission ESC 2008, Crete, Greece, September 2008.
Roth, M. and Blikra, L.H.
(2008). Seismic monitoring at the Åknes rock slope, Norway, European
Geosciences Union General Assembly 2008, Vienna, Austria, April 2008.
5.5 Project
reports
Harmandar, E. and H. Bungum
(2007): Attenuation relationships for ShakeMap applications in Europe.
Report for the NERIES (EU) project.
Lang, D.H., Lindholm, C.D.,
and Balan, S. (2007): Seismic risk and loss assessment for a selected
study area in Bucharest, Romania. Technical report for the SAFER
project, April 2007, 25 pp.
Molina, S., Lang, D.H., and
Lindholm, C.D. (2007): SELENA v1.1 - User and Technical Manual v1.1,
February 2007, 45 pp.
Molina, S., Lang, D.H., and
Lindholm, C.D. (2007): SELENA v2.0 - User and Technical Manual v2.0, May
2007, 59 pp.
Molina, S., Lang, D.H., and
Lindholm, C.D. (2007): SELENA v3.0 - User and Technical Manual v3.0,
December 2007, 69 pp.
Molina, S., Lang, D.H., and
Lindholm, C.D. (2008). SELENA v3.5.1 - User and Technical Manual v3.5.1,
May 2008, 69 pp.
Molina, S., Lang, D.H., and
Lindholm, C.D. (2008). SELENA v4.0 - User and Technical Manual v4.0,
October 2008, 85 pp.
Lang, D.H., Gutierrez, V.,
and Lindholm, C.D. (2008). RISe v1.0 - User and Technical Manual v1.0,
December 2008, 22 pp.
6
Personnel
Hilmar Bungum
Amir M. Kaynia
Daniela Kühn
Dominik Lang
Conrad Lindholm
Sergio Molina
Volker Oye
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