Part 1: Geologic Hazards
Introduction:
Hazards are natural process which happen whether or not humans are present. For all natural hazards we’ll begin with a brief overview of the physical processes, the spatial extent and region, and the temporal duration and frequency. This course begins with geological hazards, all of which are generated by tectonic activity. These hazards include earthquakes, volcanoes, tsunamis, and landslides.
Physical Processes: The forces of natural phenomena
Earthquakes happen at faults. A geologic fault is similar to an electrical fault. In both cases, energy fails to flow smoothly or continuously. Although there are different types of faults, all quakes are measured the same way, in terms of magnitude. The energy involved in a quake moves through earth in waves. The amplitude, frequency, period, and depth of the waves contribute to the damage caused. The stronger and the closer the waves are, the more damage results.
The scales for measurement have changed over time. The Richter scale, which ranged from 1 to 9, relied on distance and depth of the waves. Scales now have no limit and account for ground type, land-use, and socio-economic factors, in order to give us an idea of the expected damages associated with the physical hazard components tailored to the affected area.
The physical forces that generate an earthquake build over time and fault when the pressure can no longer be held. Scientists monitor pressure on faults to predict the likelihood of an earthquake or an aftershock. An earthquake may actually cause a sequence of aftershocks, as pressure shifts from one part of the fault to another. These sequences can last for years. The aftershocks are characterized as smaller earthquakes triggered by a larger initial event. Even this brief introduction shows that physical earthquake conditions are related to the spatial distribution and the temporal rates of distribution.
Watch this introductory video from National Geographic to learn more about earthquakes:
Spatial: Impacted and Predicted area. Where did it happen?
The spatial extent of earthquake activity is centered around the Earth’s active faults where mountain ranges are still rising and trenches are sinking. The extent of the impacted area varies from event to event.
Some faults run for hundreds of miles, and a rupture can extend out from the original fault into connected smaller faults if the intensity is high enough. Other less intense events are limited in area. The real extent of an event is, consequently, related to its physical components.
To get an idea of the global risk and efforts to reduce the risk, view the video:
Episode 4: Earthquakes Exploring Early Warning Systems
Several temporal components are important when discussing earthquakes. The duration of the event is related to the damage that occurs. The longer the shaking, the more destruction is likely to occur. Earthquakes usually last a matter of seconds but have been recorded for several minutes. The event frequency is related to the spatial component. Earthquakes are more frequent around active plates. The 2011 Virginia earthquake was an unexpected event, because the faults in this area are not often active. The Spokane area has small quakes every few weeks.
There is no earthquake season. Earthquakes do not occur at specific times of the day either, but the diurnal factor does influence the death toll. Earthquakes that occur at night are usually less deadly because people are at home instead of working or gathering in large numbers in high-rise buildings. Earthquakes result from pressure building on a plate, so their rate of onset could be said to be hundreds of years between faults, but these geologic terms are not usually what people think of when they are discussing earthquakes. They think of the warning period for the actual event, which is a matter of seconds or minutes. Scientists are still trying to extend warning periods for earthquakes. This will be discussed further on the next page.
Earthquake Measurement Systems
It is difficult to predict earthquakes. Most areas receive no warning in advance of an earthquake. Due to this short warning, the best way to get ready for an earthquake is to hide under a desk, or go to an open area away from buildings to protect yourself from falling debris. Exiting a tall building from an upper story or going into a street between buildings during an earthquake is not safe. This can be an issue if building shaking is misinterpreted as an attack and occupants react by running out of buildings. This is an example of the social amplification of risk. Panicked building occupants can spread incorrect information and endanger others by having them follow them.
Areas with frequent earthquakes have systems that can detect tectonic activity likely to result in an earthquake approximately a minute in advance. Studies of areas like New Zealand’s Alpine Fault continue to try to increase the amount of time, prior to an earthquake, that a warning can be sent. See this video for more information about drilling into New Zealand’s most dangerous fault:
Author: Nicole Hutton, Ph.D. via Canvas Commons course from Old Dominion University. Edits and revisions by Cameron McCormick
