Tuesday, September 29, 2015

GIS and Earthquakes

GIS Mapping of Earthquake-Related Deaths and Hospital Admissions from the 1994 Northridge, California, Earthquake

Earthquakes pose a serious risk to human health and the public’s safety. Earthquakes have the potential to destroy entire cities and kill thousands of people in just the matter of a few minutes. The article by Peek-Asa et al. (2000) was a study done on the 1994 Northridge, California earthquake that devastated the city. The history of that deadly earthquake is described below for better understanding of the author’s experiment.

The basic background of earthquakes has to be taken into account in order to comprehend the methods used in this study. Earthquakes are tremors and shaking in the earth’s crust caused by seismic activity, which is the sudden release of energy.
In regards to the Northridge quake, it was located in California in an earthquake prone area. While the earthquake had a duration of only 10-20 seconds, it had a moment magnitude of 6.7. This was the highest ground acceleration ever instrumentally recorded in a North American urban area. The tremors were felt as far away as Las Vegas, Nevada, which was about 220 miles away from the epicenter. The epicenter was located in the San Fernando Valley, about 20 miles northwest of the downtown area of Los Angeles.
There were several thousand aftershocks after the main quake, some of which were quite large still. The death toll was 57 people, while there were more than 5,000 injured. Furthermore, the Northridge quake amounted to approximately $13-$40 billion in property damage.

First and foremost, earthquakes are extremely unpredictable and there is little warning when one is about to occur. The authors of this study desired to study the spatial relations between the injuries sustained by people and the seismic activity and location of the earthquake. Considering earthquakes pose such a massive health threat, the authors found that there was significance in researching the relations of seismic hazards and building damage to the risk of injury of a person.
To accomplish this, fatal deaths and those injured and admitted to hospitals were identified and pinpointed. Then, all injury locations were charted on map of the area using GIS methods and software. Subsequently, injuries were analyzed in regard to the distance from the epicenter of the earthquake, as well as other factors such as the proportion of damaged buildings in the area, and peak ground acceleration.

The results from the Peek-Asa et al. (2000) study were that injury severity was inversely related to the distance from the epicenter (i.e. more injuries occurred in areas closer to the epicenter, and less injuries occurred farther away from the epicenter), and in addition, increased with cumulative ground motion and building damage. However, the study did not show that injury severity and incidence were completely predicted by the building damage and the seismic hazard.
They also predicted that outside factors such as age and the activity of the person during the earthquake could have affected the severity of injury (such as driving a car). The figure below shows the injury locations in regards to how intense the quake was in that specific area, as well as the proportion of damaged residential structures. Furthermore, Peek-Asa et al. (2000) found that injuries of all severities occurred over a wide range of distances from the epicenter of the quake. They discovered that rescue efforts cannot be solely focused on the immediate damage zone.


Peek-Asa, C., Ramirez, M. R., Shoaf, K., Seligson, H., & Kraus, J. F. (2000). GIS mapping of earthquake-related deaths and hospital admissions from the 1994 Northridge, California, earthquake. Annals of Epidemiology10(1), 5-13.

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  1. Good job. I would like to know more about the minimum requirements they give to count as injured. It affects the data a lot depending on where they cut it off. Or was it just hospital admissions regardless whether the injury warranted it? Another question I have is how has this data affected post-earthquake aid efforts?

  2. I like how you analyzed the image and described what the graph was portraying. Did anyone go missing? It would seem like some people would not be accounted for. Would they just be added to the death toll automatically? Also, were the layouts of the structures altered after the earthquake to avoid another disaster?