What earthquake hazards exist in high risk states?
High risk states have known active fault systems that produce periodic moderate to strong earthquakes. These may include intraplate faults, extensions of major fault systems, or regions with historical seismicity. Utah, Nevada, and Hawaii fall into this category, each with distinct seismic sources.
How frequently do earthquakes occur in high risk states?
High risk states typically experience felt earthquakes (M3.0+) several times per month and potentially damaging events (M5.0+) every few years. The frequency varies by specific region within the state.
What building codes apply in high risk earthquake states?
High risk states generally adopt the International Building Code (IBC) with seismic provisions requiring structures to withstand expected ground motions. Newer buildings incorporate base isolation, reinforced concrete, and flexible steel framing. Older structures may need retrofitting.
What causes earthquakes?
Earthquakes are caused by the sudden release of energy in the Earth's crust, usually due to the movement of tectonic plates. When stress accumulates along a fault line faster than it can be released through slow creep, the rocks eventually fracture and slip, generating seismic waves that we feel as an earthquake.
How are earthquakes measured?
Earthquakes are measured using seismographs that detect ground motion. The magnitude (energy released) is calculated using various scales including the moment magnitude scale (Mw), which has replaced the Richter scale for most purposes. Intensity (effects on people and structures) is measured using the Modified Mercalli Intensity (MMI) scale.