Seismic Loss Assessment in Algeria Using the Tool QLARM- Juniper Publishers
Juniper Publishers- Journal of Civil Engineering
Abstract
Beginning in 2003, QLARM (Quake Loss Assesment for
Risk Management] has been used for real-time loss estimation and one
hour after the M6.7 Boumerdes earthquake in 2003, we reported 1690-3660
fatalities, when the official death toll was weeks later announced as
around 2270.
We have estimated losses for past earthquakes in Algeria that occurred
during the period 1990-2003 finding that reported values of fatalities
and injured were within the range of the calculated ones. Earthquake
loss scenarios for Oran, Algiers and Djidjelli assuming repeats of
events that occurred in the past, but with today’s population, indicates
thousands of fatalities (from 5,000 to 24,000], depending on the
scenario and the time of earthquake occurrence (day or night], with the
number of patients expected about 4 times in average the number of
fatalities. Amplifications of the accelerations due to soil conditions
in different cities could increase casualty numbers by 10 to 40%,
depending on the scenario.
Keywords: QLARM; Seismic risk; Algeria; Scenarios; El Asnam; Earthquakes
Introduction
Since the 1980 El Asnam earthquake, seismic events in
Algeria have killed about 6,000 people, injured more than 20,000 and
left more than 300,000 homeless. Economic losses were estimated to have
been up to 2 billion dollars for the El Asnam event and around 5 billion
dollars for the 2003 Boumerdes M6.8 earthquake. Damage to buildings is
expected for events with magnitude around 5.5 and on average, one
earthquake with the potential to kill people (M>5.4] happens every
three years in
Algeria. In order to help risk management, we built the QLARM database
to estimate human losses in Algeria in the case of major earthquakes [1].
Algeria had enough historic earthquakes for building damage,
intensities, fatalities or injuries were reported, such that we were
able to validate our computer tool. Therefore, we feel confident that
our loss estimates for future earthquakes are reasonably reliable,
within the large margins of uncertainties that are associated with a
scenario exercise like this.
Seismic Wave Propagation Model
Among other intensity prediction equations used for Algeria, the Shebalin [2]
one was able to fit the observations best for all the tested
events-Tipaza (1989], Mascara (1994], Benian (1996], Temouchent (1999],
Ourtilane (2000] and Boumerdes (2003]. Site condition in each settlement
of the database is approximated using Vs30 derived from slope topography [3].
Most of the settlements (62%] are classified as soil type D (stiff
soil] and others range from soft to hard rock. The amplification factor
given by NEHRP [4]
for each soil type is converted to an additional intensity value using
the ground motion-intensity conversion equation of Wald et al. [5]. The added intensity values are 0, 0.16 and 0.32 for soil type B, C and D respectively.
City Model
City Model
The dataset in QLARM for Algeria is composed of 1540
settlements. Population comes from the 1998 and 2008 census (Office
National de la Statistique] and updated for 2013. The
distributions of population and buildings into vulnerability classes (Figure 1)
is estimated by considering the fractions of the residential population
(in %) and the peak average number of occupants per building as given
by the World Housing Encyclopedia [6] and PAGER database [7].
These distributions are provided for three city sizes-large urban,
medium urban and rural-2,000 and 20,000 people as limits. For rural
settlements, we consider an occupancy rate of 30% during the day (6am-
6pm) and 95% during the night. For urban settlements, these values are
changed to 50 and 80 % respectively.
Estimated Losses in Repeat Earthquakes
QLARM calculates building damage divided into five
degrees, mean damage grade and the range of fatalities and injuries for
each settlement around the epicenter [8-10].
It also calculates the strongly affected people, those that live in the
area of shaking with intensities VI+, level of shaking when damage to
dwellings and injured likely result in Algeria and other regions with
poor construction. After calibrating QLARM as mentioned, three scenarios
that correspond to past damaging earthquakes in the vicinity of the
largest cities of Algeria were selected as listed in Table 1.
Populations in the areas with intensities VI plus VII and in
intensities VIII+ are also shown because the damage and the casualties
are significantly different (Figure 2).
Discussions
We propose a dataset and city model calibrated and
validated for Algeria in QLARM in order to help in seismic risk
management. It includes 1504 settlements for which population, building
stock and site conditions are defined. The conclusion of this work is
that QLARM can be used to calculate damage and casualties correctly to
within a factor of about two. Three scenarios based on the repetition of
historical earthquakes are proposed (Table 1).
Our loss estimates could be refined, made more accurate and more
detailed by collecting data on site amplification in the largest cities,
by constructing discrete city models for important cities and by
defining a set of seismic line sources but also other seismic point
sources with lower magnitude.
Acknowledgement
Acknowledgement
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