Geographic Distribution of Earthquakes Earthquakes are distributed unevenly on the globe. In certain places they are more frequent and intense whereas in other places they are extremely rare and feeble or their effect is hardly perceptible Studies on the occurrence of earthquakes on the globe have indicated that there are certain zones within the continents along which seismic shocks are felt rather frequently
MSK is the seismic intensity scale used to evaluate the severity of ground shaking. It has 12 intensity degrees MEDVEDAV-USSR SPONHEUER-EAST GERMANY KARNIK - CZECHOSLOVAKIA
The Indian subcontinent has a history of devastating earthquakes. The major reason for the high frequency and intensity of the earthquakes is that the Indian plate is driving into Asia at a rate of approximately 47 mm/year. Geographical statistics of India show that almost 54% of the land is vulnerable to earthquakes
The earthquake zoning map of India divides India into 4 seismic zones (Zone 2, 3, 4 and 5) According to the present zoning map, Zone 5 expects the highest level of seismicity whereas Zone 2 is associated with the lowest level of seismicity The MSK (Medvedev-Sponheuer-Karnik) scale intensity broadly associated with the various seismic zones is VI (or less), VII, VIII and IX (and above) for Zones 2, 3, 4 and 5, respectively, corresponding to Maximum Considered Earthquake(MCE)
Zone 5: Zone 5 covers the areas with the highest risks zone that suffers earthquakes of intensity MSK IX or greater It is referred to as the Very High Damage Risk Zone. The state of Kashmir, the western and central Himalayas, the North-East Indian region and the Rann of Kutch fall in this zone
Zone 4: This zone is called the High Damage Risk Zone and covers areas liable to MSK VIII. The Indo-Gangetic basin and the capital of the country (Delhi), Jammu and Kashmir fall in Zone 4. In Maharashtra the Patan area (Koyananager) is also in zone 4 Zone 3: The Andaman and Nicobar Islands, parts of Kashmir, Western Himalayas fall under this zone. This zone is classified as Moderate Damage Risk Zone which is liable to MSK VII and also 7.8
Zone 2: This region is liable to MSK VI or less and is classified as the Low Damage Risk Zone Earthquake Prediction: Earth quake prediction is done by the following methods Time Interval Analysis Seismic Gap
Time Interval Analysis include laboratory and field studies of rocks before, during, and after earthquakes monitor activity along major faults produce risk assessments
Seismic Gap Look at the location of earthquakes Areas (Gaps) where no earthquake has happened is an area of accumulating strain Gaps represent locations of future earthquakes
Focuses on patterns in seismicity. Predicts based on irregular activities. Also if there is a large gap in activity on an active fault. If a change in the pattern occurs, there is a chance for an earthquake
Statistical Methods Recurrence Frequency: Collecting adequate amounts of data allows for predictions to be made as to the location and magnitude of earthquakes. Works out for smaller earthquakes but not for larger earthquakes Recurrence Frequency: Relationship between the magnitude and repetition of earthquakes. Assumes that the same set of conditions leading to an earthquake occur each time. Dependent on large amounts of historical data
Physical and Geophysical measurements and observations Studies of precursors and events that occur before an earthquake. Increase in the rate of a seismic creep and the slow movement along the fault Gradual tilting of the land near the fault zone Drop or rise in the water level of a well Decrease in the number of micro quakes and foreshocks Flashes and other lights in the sky Animal behavior
Physical and Geophysical measurements and observations Fault Creep Measurements Measures the slow rate of movement on the fault. Where lots of fault creep occur there is a small chance of a big earthquake. Where little amounts of fault creep occur there is a high chance of a big earthquake.
Physical and Geophysical measurements and observations Drop or rise in the water level of a well Large amplitude surface seismic waves force the particles of the rock near the surface to move adjusting the level in the well. Before an earthquake water wells are also affected by any fault creeps, crust tilts, or other seismic activity. Drilling wells in certain locations and measuring the water level and quality can aid in earthquake predictions.
Physical and Geophysical measurements and observations Animal behavior Recognizing unusual animal behavior in a systematic way can be used to predict earthquakes The Chinese started recording unusual animal behavior and successfully predicted an earthquake in 1975 3 months before it struck.
Physical and Geophysical measurements and observations Unusual animal behavior: Hibernating animals leaving their underground nests Animals refusing to go into pens Animals seeking higher ground Birds vacating the area Deep water fish come closer to the surface
Conclusion No 100% accurate way to predict an earthquake. As more data is collected, predictions will get better. From data mining, more patterns will be found increasing the accuracy of predictions.