What causes damage during an earthquake?
• Duration of shaking. Duration depends on how the fault breaks during the earthquake. The strongest shaking during the 1964 earthquake lasted 3 to 4 minutes. During a magnitude 7 earthquake, the shaking may last 30 to 40 seconds. The longer buildings shake, the greater the damage. • Strength of shaking. Many damaging earthquakes occur within 15 miles of the Earth’s surface. In this case, shaking decreases rapidly with increasing distance from the fault that produced the earthquake. In Alaska, these are most common in central and southeastern Alaska. Deeper earthquakes are common beneath southern Alaska and the Aleutian Islands. Because of their greater depth, the shaking directly above such shocks is reduced, and the shaking decreases gradually with increasing distance from the epicenter of the earthquake. • Type of soil. Shaking is increased in soft, thick, wet soils. In certain soils the ground surface may settle or slide. Damage is reduced in buildings located on bedrock. • Type of
