Seismic Hazards In the Region of Japan and Indonesia Essay

Seismic Hazards In the Region of Japan and Indonesia - Essay Example ‘Seismic Hazards’ and ‘Seismic Risks’ are often confused with one another. Seismic hazards may also be defined as any physical phenomena (for example, ground shaking) that are associated with an earthquake and that may produce adverse effects on human activities. It is restricted to the study of likely earthquake ground motions at any point on the earth. Seismic risk constitutes the results of a seismic hazard analysis, including both the consequence and the probability. Seismic risk is used to describe earthquake effects that include ground shaking, surface faulting, landslide, and economic loss and casualties (Algermissen 1). The following statement may help to distinguish between a hazard and a risk: Â   Â  A building located in a region of high seismic hazard is at lower risk if it is built on the basis of sound seismic engineering principles; whereas, a building located in a low seismic hazard zone is said to possess a high risk if not built in accord ance to the seismic engineering principles applicable to that zone.‘Seismic Hazards’ and ‘Seismic Risks’ are often confused with one another. Seismic hazards may also be defined as any physical phenomena (for example, ground shaking) that are associated with an earthquake and that may produce adverse effects on human activities. It is restricted to the study of likely earthquake ground motions at any point on the earth. Seismic risk constitutes the results of a seismic hazard analysis, including both the consequence and the probability. Seismic risk is used to describe earthquake effects that include ground shaking, surface faulting, landslide, and economic loss and casualties (Algermissen 1). The following statement may help to distinguish between a hazard and a risk: A building located in a region of high seismic hazard is at lower risk if it is built on the basis of sound seismic engineering principles; whereas, a building located in a low seismic hazard zone is said to possess a high risk if not built in accordance to the seismic engineering principles applicable to that zone. Probabilistic Seismic Hazard Analysis (PSHA) PSHA quantifies the probability, rather the rate, of exceeding the level of various ground motions at a site given all possible earthquakes (Field). Cornell was the first seismologist to develop this numerical approach to PSHA in 1968. PSHA involves three steps: 1. Specification of the seismic-hazard source model. 2. Specification of the ground motion model. 3. The probabilistic calculation. Hazard curves developed through PSHA show the likelihood of exceeding the various ground motion values at a specific site; on a typical hazard curve 10% probability of exceedance in 50 years is considered as one point. Actually, there is no alternative for a hazard curve to compare hazards at different locations. These curves are crucial in helping us to understand different types of ground motions. Not only this, the hazard c urve helps to determine the expected losses. Losses can occur from both frequent smaller events or from less frequent large events. An annual rate of exceedance versus peak ground acceleration (PGA) is defined as a hazard curve plot. An example is shown below: Seismic Hazard Analysis of Japan A group of island arcs related to various subduction zones constitute Japan. These islands stretch from the Kurile Islands in the northeast to the Ryukyu chain in the south. Japan uses its own seismic scale, in units of Shindo, to measure the strength of earthquakes. The JMA scale differs from other seismic scales in the way that it describes the degree of shaking at a given point on the Earth's surface. The magnitude of JMA scale is measured between 0 and 7. The JMA reports of earthquake level are based on the peak ground acceleration (PGA). A relationship of Shindo Number along with PGA and the effects on people, Ground and Slopes and Outdoor Situations (JMA) is represented in the Table below : Shindo Number Peak Ground Acceleration (PGA) People Grounds & Slopes Outdoor Situations 0 Less than 0.008 m/s? Imperceptible to people. 1 0.00