Tectonic Hazards Can Be Successfully Managed. Discuss.

Tectonic hazards can be successfully managed. Discuss (40 marks)

A hazard is a risk to people and/or their property and tectonic hazards are those that result from the processes originating in the earths lithosphere and asthenosphere. Volcanic eruptions, earthquakes and tsunamis can all potentially represent a hazard and people have devised various strategies for managing them. Successful management would include prediction (location, timing, intensity) and reducing the vulnerability of people and their property (education and engineering).  The degree to which this can be done successfully will be discussed.

Although earthquakes can be reasonably well modelled using the elastic rebound model the time at which the energy is released at the fault line is almost impossible to predict. It was once thought that micro quakes appear as precursors to a major event. The USGS used this model to make what they thought was a confident prediction for a magnitude 6 earthquake in the town of Parkfield, California in 1993. A network of strain gauges (to measure deformation) and seismometers (to measure shock waves) was established in order to gather data used to make this prediction. It never happened and in fact the next major earthquake was a magnitude 6 in this area in 2004. This earthquake had no precursors. Loma Preita, California was another region identified where lack of seismic activity over many years suggests a “seismic gap” in this region and thus a great amount of strain was building up leading to a potentially higher magnitude event. Scientists were unable to predict when the next quake would occur. In 1989 a magnitude 6.9 occurred killing 63 people.

Latest management is Now-Casting. Automated systems are being trialled in San Francisco including the shutting down of gas pipes and instant text messaging to citizens in the city giving an estimated time (seconds to minutes) of an arriving earthquake. This works on the principle that the first waves to arrive are p waves which are lower magnitude and less destructive because of their longitudinal direction of force. The s and l waves arrive seconds to minutes later depending on the distance to the epicentre thus it is possible to warn in advance of the arrival of the more destructive surface waves.

Strict building codes in San Francisco were brought in in 1970 and modern skyscrapers are earthquake “proof” via techniques such as base isolation which reduce the transfer of shock waves from the foundations to the building itself. However, 80% of the city’s housing was built before 1970 and typical houses have a garage underneath and then residence above which makes them top-heavy and vulnerable. The bay area of San Francisco is built on mud and vulnerable to liquefaction and thus could experience severe damage like that witnessed in the port area of Kobe, Japan, 1995. Since San Francisco is still waiting for the “big” one, evaluation of the effectiveness of these strategies is problematic but because many residential housing is built pre-1970, the loss of life and property with a magnitude 9 earthquake could be massive.