Earthquake casualty estimation

Recent advances are improving the speed and accuracy of loss estimates immediately after earthquakes (within less than an hour) so that injured people may be rescued more efficiently.

After major and large earthquakes, rescue agencies and civil defense managers rapidly need quantitative estimates of the extent of the potential disaster, at a time when information from the affected area may not yet have reached the outside world.

The estimates of fatalities distributed by email by the QLARM team of the International Centre for Earth Simulation Foundation (ICES)[6] within 100 minutes of the Wenchuan earthquake[5] was 55,000 ± 30,000, which includes the final toll of about 87,000.

[10] For most of the world, this luxury is not available and the worldwide seismograph network[11] has to be used to estimate the location based on teleseismic data[12] (recorded at distances of more than 1,000 km).

The following agencies distribute estimates of latitude, longitude, depth, and magnitude of worldwide earthquakes rapidly and with high accuracy.

The decrease of the wave amplitudes as a function of distance (Figure 2) shows that dangerous intensities, I≥VII, do not exist beyond 30 to 50 km for major earthquakes.

The teleseismic method is to measure the time delay with which the wave reflected from the Earth's surface above the earthquake arrives at a seismograph.

This method works fine, if the hypocentral depth Z>50 km because, in that case, the direct and reflected phases (waves) are clearly separated on the record.

For earthquake with magnitudes smaller than M7.5, the different agencies mentioned above as issuing location estimates, usually distribute values of M within 0.2 units from each other.

In these cases, an in depth analysis, which takes time, is needed to arrive at the correct M. As an example, the Wenchuan earthquake of 12 May 2008 had originally been assigned M7.5 in real-time.

The standard teleseismic measure of the 'size' of an earthquake is the surface-wave magnitude, Ms, which has to be derived by definition from the surface waves with 20 second period.

Shaking of the ground decreases with distance from the release of energy, the hypocenter, or, more accurately expressed, from the entire area of rupture.

In the immediate aftermath of the Haiti earthquake of 12 January 2010, a joint study for the estimation of damage to the building stock based on aerial images was carried out by UNITAR-UNOSAT, the EC-JRC, and the World Bank/ImageCAT in support of the PDNA.

Hancilar et al. (2013) have developed empirical fragility functions based on remote sensing and field data for the pre-dominant building typologies.

The probability that a building of a given type may collapse if subjected to a certain intensity of shaking (Figure 5) is an important parameter for calculating expected human losses.

Data sources on the web include the World Gazetteer,[34] the National Geospatial-Intelligence Agency (NGA), and GeoNames for population by settlements.

The time when the consequences are less serious are the morning and evening hours, when farmers are out of doors and office and factory workers are commuting.

If one wanted to estimate in real time what damage is to be expected for critical facilities (e.g. a nuclear power plant, a high dam of a reservoir, bridges, hospitals, schools) one would have to know quite a few additional details.

In estimating losses in real time, one must take advantage of the fact that some buildings are built to code, others are not, some are located on hard rock, others on unconsolidated sediments, and the earthquake may radiate more energy in one direction than in another.

With this added information, it is possible to better classify the construction type of each building and to deepen the detail of the model of the built environment necessary for accurate estimates of losses due to earthquakes.

If one has the resources to divide a large city into neighborhoods containing similar building stock, then a high quality model can be constructed at a still moderate cost.

An example of the mortality rate estimates in case of a future M8 earthquake off Lima, Peru, shows that there are substantial differences between districts (Figure 9).

In addition to the mortality calculation for the entire population, information on the locations and expected damage state of schools, hospitals, fire stations, police posts, and critical facilities would be of great value for rescuers.

In some cities, elaborate efforts by commercial enterprises have been carried out or are under way to catalog information on a neighborhood level, more detailed than shown in Figure 9.

[39] By email, the QLARM team is distributing estimates of human losses (numbers of fatalities and injured), in addition to calculations of mean damage for each settlement in their database, following earthquakes worldwide since October 2003.

[4] Recent alerts can be found on the web page of the International Centre for Earth Simulation Foundation (ICES), Geneva.

[41] They contain a color code reflecting the seriousness of the event, the number of people estimated to have been exposed to the various likely intensity levels, tectonic information about the epicentral area, and consequences that had resulted from previous nearby earthquakes.

This information can be misleading because the parameters, which control the extent of a disaster, are ignored (magnitude, depth, transmission properties, building stock characteristics, and time of day).

Inconsequential events can be identified in 99% of the cases, which means that rescue teams do not need to waste time and energy to needlessly mobilize.

Although the uncertainties in estimating human losses in real time are large,[15] they allow one to immediately identify disastrous cases that need attention.