Which is used determine earthquake risk?

Answer 1

Strains in rocks near faults

Answer 2

The earth's crust has many major fault areas where the risk of earthquakes or volcanic activity remain very high. One such area is the "Ring of Fire", which extends from the Pacific Coast at Asia, around to Alaska, down the western USA coast, and over to the Carribean. Most earthquakes happen along that "Ring" including underwater volcanoes. A second major fault line is at New Madrid, Missouri, USA.

Incidence

Every day, very small tremors occur in many places. The earth's mantel is constantly moving along fault lines where the earth is "fractured". One type of fault line "slides" along each other until it cannot move further. However, the pressure still builds even when the two surfaces aren't moving, resulting in a much larger earthquake when the pressure releases. Another type of fault rarely moves but in its stationary position, greater forces build up below and between the fault line, again causing very large quakes when the surfaces finally move past each other. The recent earthquake in Haiti took 200 years to build pressure against the two surfaces of the fault line. The last major earthquake at New Madrid, Mo. was in approximately 1812. Newspapers report that the quake was felt as far away as the Atlantic shore and caused the Mississippi River to flow backwards. The earthquake that hit California in the 1980s or 1990s was a "small" quake compared to the one at New Madrid.

Thus, the earth's ever-changing mantel and layers along fault lines is the greatest risk factor in producing an earthquake. Also, seismolgists have shown that quakes follow quakes. Not only are there after-shocks, a massive earthquake can cause faults in other locations to move, thus producing quakes in other areas weeks, months, or years later. A "few years" in geology is miniscule compared to millions of years for most geological events, so a quake following in "a few years" is a very, very short period of time.

Effects

Even small earthquakes can cause massive damage to buildings and bridges if these are constructed poorly. The types of buildings in Haiti were baked earthen and cement structures with no steel or rebar reinforcement. Engineers say that buildings with reinforcement can more easily sway but not crumble, while un-reinforced concrete or earthen materials simply collapse. The weight of material cascades down, breaking apart any material below it, as seen in Haiti recently. Numerous injuries and deaths result from the collapsing structures, more than from the earth moving while people are outside the structures. However, falling debris (bricks, mortar, etc) can also kill.

As well, we saw how even in developed areas like California, with reinforced concrete bridges and buildings, there can be massive collapses of infra-structures. The main Interstate with multiple levels "pancaked" as each tier collapsed. One of the biggest concerns in California centers on how well their aging but multi-tied bridges will withstand the next "big one".

Future

While most people focus on California, USA, scientists repeatedly warn about the potential of a large new quake at New Madrid. They predict the devastation could be massive since there is a large population in that area. And a quake at New Madrid could change the beds of streams, creeks, and rivers, similar to the changed coastline that occurred at Haiti.

Answer 3

Seismic hazard analysis is typically used to determine earthquake risk by identifying potential sources of seismic activity, estimating the likelihood of future earthquakes in a specific area, and predicting the level of ground shaking that may occur during an earthquake. This information is used to inform building codes, emergency preparedness plans, and other measures to mitigate the impact of earthquakes.

Answer 4

The movement of seismic waves along faults and friction.

Answer 5

the answer you will have to loook in a book to find i am the only one that can look it up on the internet

Answer 6

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