Presentation on theme: "Location and Damage from EQ. Where EQ Occur Most EQ occur at plate boundaries More EQ occur at transform faults than at other plate boundaries Most."— Presentation transcript:
Location and Damage from EQ
Where EQ Occur Most EQ occur at plate boundaries More EQ occur at transform faults than at other plate boundaries Most EQ that occur at transform faults and mid- ocean ridges are shallow-focus. They happen very close to the surface of the earth. Most EQ that occur at subduction zones are usually deep-focus EQ They happen very far below the surface of the earth
Areas of Risk Risk is the impact natural hazards have on people. Factors that affect risk are the size of the hazard, how often they occur, how close they are to people, and how many people live in the area. Highest risk for EQ is at plate boundaries. EQ can also occur away from plate boundaries in weak areas of crust. –Stress in crust affects the entire plate, and weak areas of the crust can break because of stress at the edges.
EQ Hazards Direct hazards –The main effect of a hazard, like the shaking of the ground caused by an EQ. –Ground shaking causes broken pipelines, power lines, roads, bridges, buildings, etc. Indirect hazards –Damage that is caused by something that happened as a result of the ground shaking. –Fires caused by broken pipelines and power lines can cause extensive damage after the shaking has stopped. –Other examples are landslides, lack of water, and tsunamis.
Buildings and Ground Motion Many factors affect the amount of damage that structures will have after an EQ –1. Duration of shaking The longer the EQ lasts, the more likely it is there will be severe damage. –2. Direction of Motion Many structures are built to withstand movement in a certain direction based on past EQ Movement in another direction can cause severe damage to buildings, just like in the Northridge EQ.
–3. Earth materials Buildings on filled material, such as loose, wet soil, are more damaged because the amplitude of the seismic waves is bigger. In the 1985 EQ, Mexico City sustained a lot of damage because it is built on volcanic ash and gravel, sand, and clay. Acapulco was much closer to the epicenter, but had very little damage because it is built on solid bedrock. –4. Resonance Happens when the shaking of the ground matches the natural sway of a building, making it sway more. This causes severe damage to the building. –5. Building materials The type of material used to build a structure can help it withstand an EQ. Wood, stone, brick, concrete, and adobe all have different responses to shaking.