Why do rock break? Review three types of stress: tension, compression, shear Three types of deformation resulting: elastic, plastic and brittle We’re concerned with the brittle deformation – causes faults, fractures through which energy, created by the friction, is released Define Focus, epicenter and seismic waves
A drop of water – analogy between ripples in the water and seismic waves
P-waves: the bell analogy: waves felt by both sound
Earliest seismograph was invented in China ~ 2000 years ago (or 136 AD) Easy to make; can make your own at home
Write Table 11-1 on the board, to help relate to Richter scale
A large mass of ice and rock separated from a vertical face on Nevado Huascaran, the highest peak in Peru The slab fell 1000 m vertically, disintegrated, slid down the lateral slopes of the mountain, and then was launched off a 'ski jump'. Debris reached a velocity as high as 280 km/hr buried the towns of Yungay and Ranrahirca, having traveled 11 km horizontally in about 4 minutes at a mean velocity of 165 km/hr. The death toll in both villages was 20,000.
Animals and earthquakes: On February 4, 1975 the Chinese successfully evacuated the city of Haicheng several hours before a 7.3 magnitude earthquake-- based primarily on observations of unusual animal behavior. Conventional science has never been able to adequately explain the phenomenon. Although the majority of accounts pertain to dogs and cats, there are also many stories about other types of animals in the wild, on farms, and in zoos; including horses, cows, deer, goats, possums, rats, chickens, and other birds. The behavior has been reported in many other animal species as well, including fish, reptiles, and even insects. Deep sea fish, for example, have been caught close to the surface of the ocean on numerous occasions around Japan prior to earthquakes (Tributsch, 1982). A number of theories have been proposed to explain this phenomenon, and what the precursory signals that the animals are picking up on might be. Because many animals possess auditory capacities beyond the human range, it has been suggested that some animals may be reacting to ultrasound emitted as microseisms from fracturing rock (Armstrong, 1969). Another candidate is fluctuations in the earth's magnetic field. Because some animals have a sensitivity to variations in the earth's magnetic field (usually as a means of orientation), and since variations in the magnetic field occur near the epicenters of earthquakes (Chapman and Bartels, 1940), it has been suggested that this is what the animals are picking up on.
Assigns an intensity or rating to measure an earthquake at a particular location ( qualitative)
I (not felt) to XII (buildings nearly destroyed)
Measures the destructive effect
Intensity is a function of:
Energy released by fault
Geology of the location
Surface substrate: can magnify shock waves e.g. Mexico City (1985) and San Francisco (1989)
Frequency of Occurrence of Earthquakes ¹ Based on observations since 1900. ² Based on observations since 1990. 1,300,000 (estimated) 2 - 2.9 Very Minor 130,000 (estimated) 3 - 3.9 Minor 13,000 (estimated) 4 - 4.9 Light 1319 ² 5 - 5.9 Moderate 134 ² 6 - 6.9 Strong 17 ² 7 - 7.9 Major 1 ¹ 8 and higher Great Average Annually Magnitude Descriptor
Most Destructive Known Earthquakes on Record in the World 166,836 injured, 600,000 homeless . 7.7 20,023 India 2001 Jan 26 Estimated death toll as high as 30,000 Old lake bed magnified shock waves by 500% 8.0 9500 (official) Mexico Michoacan Sept 19, 1985 Estimated death toll as high as 655,000. 7.5 255,000 (official) China, Tangshan July 27, 1976 $530,000,000 damage, great rock slide, floods. 7.9 66,000 Peru May 31, 1970 Deaths from earthquake and tsunami 9.0 283,106 Sumatra 2004 Dec 26 Comments Magnitude Deaths Location Date
1) seismic hazard maps 2) probability analysis based on: - historical EQ records - geologic EQ records - slip-rate on active faults - frequency and magnitude of recent EQ's Real-time 24 Hour Forecast
Short-term predictions Precursor phenomena (<1 year to days) 1. Foreshocks: usually increase in magnitude 2. Ground deformation 3. Fluctuations in water well levels 4. Changes in local radio wave characteristics 5. Anomalous animal behavior???