Jawaharlal Nehru Technological University Hyderabad B.Tech III ELEMENTS OF EARTHQUAKE ENGINEERING Previous Question Paper (August/September - 2021 - R18)

The Plate Tectonic Theory posits that the Earth's outer shell, the lithosphere, is divided into several large and small rigid plates that float and move over the semi-fluid asthenosphere. This movement is driven by mantle convection currents generated by internal heat.

• Divergent Boundaries: Plates move apart, allowing magma to rise, creating new crust (e.g., Mid-Atlantic Ridge).
• Convergent Boundaries: Plates collide. One plate may subduct beneath another (subduction zone), leading to intense seismic activity and volcanic arcs.
• Transform Boundaries: Plates slide horizontally past each other. Friction causes stress to accumulate until it is released as an earthquake (e.g., San Andreas Fault).

Significant earthquakes resulting from these interactions include:

• 1960 Valdivia Earthquake (Chile): Magnitude 9.5, caused by the subduction of the Nazca Plate beneath the South American Plate.
• 2004 Indian Ocean Earthquake: Magnitude 9.1, resulting from subduction along the Sunda Trench.
• 1906 San Francisco Earthquake: A major event caused by the strike-slip motion along the San Andreas Transform Fault.

Earthquakes are caused by both natural and anthropogenic factors:

• Tectonic activity: Sudden release of accumulated strain energy at plate boundaries.
• Volcanic eruptions: Movement of magma beneath the surface.
• Reservoir-induced seismicity: Loading of large water bodies behind dams.
• Anthropogenic activities: Mining, underground nuclear testing, and fluid injection.

The estimation of earthquake parameters is as follows:

Magnitude (M): A quantitative measure of the energy released at the source, calculated using the Richter Scale or Moment Magnitude Scale (Mw). The formula for Moment Magnitude is:

where Mo is the seismic moment in dyne-cm.

Intensity (I): A qualitative measure of the effects observed at a specific location, typically measured using the Modified Mercalli Intensity (MMI) Scale. It ranges from I (not felt) to XII (total destruction), based on human perception, structural damage, and geological changes.