![]() ![]() Magnitude (M) is the measure of the energy released by the earthquake, whereas the intensity is what people actually experience. There are two ways to measure earthquakes: magnitude and intensity. Although the San Francisco earthquake was quite large, most of the damage to the city was actually caused by a fire, which is a common secondary hazard of earthquakes. Looking at the photo, one can visualize how the foreground moved to the left, while the background moved to the right. The fence was once connected, but today it is separated by a 6-meter (20-foot) gap. The Earthquake Trail, which begins at the Bear Valley Visitor Center, follows the trace of the 1906 San Francisco earthquake to a picket fence along the fault ( Figure 10.3). An excellent example of this kind of offset can be found along the San Andreas Fault at Point Reyes National Seashore. The plane defined by the rupture is known as a fault, and the rock layers become offset along it. The rocks then snap apart, releasing energy in the form of seismic waves ( Figure 10.2). According to the elastic rebound theory, rocks can bend elastically up to a point, until they finally break. This scale is more useful in a sense that it provides some insight into the fault plane geometry of the earthquake based on parameter $M_0$.Earthquakes occur when a critical amount of stress is applied to the crust. The magnitude( $M_0$) is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. Where $M_0$ is the seismic moment in N⋅m ( $10^7$ dyne⋅cm). The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs (adjustments are included to compensate for the variation in the distance between the various seismographs and the epicenter of the earthquake). The problem with most scales is that they become saturated after a certain magnitude.ģ scales can be named which fall in this category An earthquake measured to 9.0 is one million times stronger than an earthquake at 5.0. ![]() A difference in magnitude of 2.0 is equivalent to a factor of 1000. Some of the confusion might come from that the Richter scale is logarithmic. There are few other scales, Body wave magnitude, surface wave magnitude, but to my knowledge they also stay under 10. Related to the Richter's scale is the Moment magnitude scale, it's an updated better way to measure, but it usually produce similar values as the old Richter's scale and the two scales are often confused in media. Magnitude is also measured in different scales. Medvedev–Sponheuer–Karnik scale is used in some Asian and European countries, Russia, India, Israel etc. XII on the Medvedev–Sponheuer–Karnik scale is Very catastrophic and IX in Destructive. China seismic intensity scale (CSIS), Medvedev–Sponheuer–Karnik scale and European macroseismic scale can reach values above ten, but not 13-14. Modified Mercalli Intensity scale is a way to rate the intensity of an earthquake, but the scale ends at XII (Damage total), not at 13-14 (XIII-XIV), as mentioned. Naturally an earthquake with high magnitude would also generate high intensity, but the intensity depends on distance from the hypocenter and the local geological conditions. Intensity is determined from effects on buildings, landscape and people. Magnitude is the energy released of the earthquake. Magnitude and intensity are related but measure very different properties of the event. Earthquakes are measured for intensity and magnitude. ![]()
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