GEOL 104 Lecture Notes - Epicenter, Mid-Ocean Ridge
Document Summary
Magnitudes less than 2. 0 are not felt by humans. Moment magnitude was developed because none of the richter-like magnitudes scales adequately estimates the size of very large earthquakes. Seismographs indicate if first-motion detected is a push or pull - this can determine the type of motion on the fault. How are earthquakes distributed in therms of their epicentre. Earthquakes are not equally distributed across the earth"s surface, they tend to be around three belts. The ring of fire is the main earthquake belt. About 95% of the energy released by earthquakes comes from these three belts. The frequency for earthquakes decreases with increase of magnitude. The most frequent are shallow, the least frequent are deep. Note that most high magnitude quakes are shallow. They generate more surface waves which are more damaging. The distribution with regard to focal depth. All the earthquakes have shallow focal depths.