KNOWLEDGE BOX 4.1 THE MODIFIED MERCALLI SCALE AND RICHTER SCALE

Table 4.1 draws an approximate parallel between the modified Mercalli scale and the Richter scale based on the records of past earthquakes. If an earthquake with the same seismic wave’s amplitude was to hit the United States, a high- income country, and Haiti, a low- income country, would the report of its strength or impact based on (1) the Richter scale, or (2) the Mercalli scale be different? How so? The value reported based on the Rich-ter scale would be the same in both countries. The reported value based on the Mercalli scale would be lower in the United States than in Haiti. This is because the actual effect of an earthquake on livelihoods is dependent on the vulnerability and manageability of each country. Since the Mercalli scale is not a mathematical calculation of the actual damages caused by the earthquake but merely founded on observations, the reported value it is based upon would be lower in a rich country that is assumed to be much more resilient to absorbing the shocks of an earthquake, as compared with a poor country which is more vulnerable to the same earthquake, resulting in higher damages and destruction.

TABLE 4.1 The modifi ed Mercalli scale versus the Richter scale

Category Effect Richter scale (approximate)

I. Instrumental Not felt 1–2

II. Just perceptible Felt by very few people, mostly those on upper fl oors of tall buildings

3

III. Slight Felt by people lying down, seated on a hard surface or on upper fl oors of tall buildings

3.5

IV. Perceptible Felt by many indoors, but by only a few outside; dishes and windows rattle

4

V. Rather strong Generally felt by everyone;

sleeping people may be awakened

4.5

VI. Strong Trees sway, chandeliers swing, bells ring; some damage from falling objects

5

VII. Very strong General alarm; walls and plaster crack

5.5

scale itself does not refl ect the severity of the impact upon human populations.

The other common scale used for earthquakes is the Mercalli scale , which indi-cates the amount of damage and destruction from an earthquake. The scale has no mathematical basis and is composed of 12 levels of increasing intensity that range from imperceptible shaking to catastrophic destruction (United States Geological Survey [USGS], 2013) (see Knowledge Box 4.1).

What are the known risk factors associated with adverse health outcomes?

The main factors associated with the adverse health outcomes of an earthquake include: the level of seismic hazard, population density and the concentration of buildings. In general, settlements located in earthquake-prone regions, or seismic belts, are at a higher risk of earthquakes. The higher the population and building density, the greater the damage may be. Figure 4.1 illustrates where several tectonic plates meet and the resulting high seismic activity. The timing of an earthquake may also be related to the magnitude of damage it brings to the community. More casualties are expected if an earthquake occurs at midnight since people are not able to react immediately while sleeping (Chou et al., 2004). Figure 4.1 is a map show-ing the distribution of earthquake- prone regions around the globe, also known as seismic belts, where there is a higher risk of earthquakes.

Category Effect Richter scale (approximate)

VIII. Destructive Felt in moving vehicles;

chimneys collapse; poorly constructed buildings seriously damaged

6

IX. Ruinous Some houses collapse; pipes break

6.5 X. Disastrous Obvious ground cracks;

railroad tracks bent; some landslides on steep hillsides

7

XI. Very disastrous Few buildings survive; bridges damaged or destroyed; all services (electricity, water, sewage, railroad) interrupted;

severe landslides

7.5

XII. Catastrophic Total destruction; objects thrown into the air; river course and topography altered

8

Source: Adapted from USGS (2013).

What are the direct health impacts of an earthquake?

The majority of the health impacts of an earthquake stem from the collapse of buildings and infrastructure. Falling debris and entrapment may directly cause trauma, crush injuries and fractures to victims. Cuts and bruises are expected for most of the patients admitted to the hospital during the fi rst week. Other associated health risks of entrapment include: hypoxia (lack of oxygen), hypo-thermia (especially during winter) and electrocution. Debris from collapsed infrastructure may also cause dust inhalation, which in turn may trigger acute respiratory distress.

FIGURE 4.1 Global seismic hazard map

Source: Global Seismic Hazard Assessment Program (http://www.seismo.ethz.ch/static/

GSHAP/global/).

What are the response needs?

Search and rescue are fundamental to the immediate earthquake response. The most successful rescues are carried out by the immediate action of nearby survivors dur-ing the fi rst phase of the disaster, when the chance of survival is the highest (see Case Box 4.1). Medical services are also needed to manage the casualties caused by the earthquake. A high volume of injuries and fractures is expected in the fi rst weeks after an earthquake. Entrapped individuals face the risks of oxygen defi cit, hypothermia, gas leak, smoke, water penetration and electrocution. Orthopaedic surgeons, anaesthesiologists, nephrologists or physicians specialising in renal care are all important specialisations required at the initial phase of disaster relief as patients with crush injuries may develop acute kidney failure (see Knowledge Box 4.2).

Since earthquakes bring huge destruction and damage to buildings, management of the homeless population is also crucial (Portilla et al., 2010).

FIGURE 4.2 Survival rates (%) of extricated people by rescue time after Tangshan earthquake in 1976

Source: Yuan (2001).