A very shallow and a deep earthquake occur simultaneously at equal distances of $40\text{ km}$ from a station. Which one of the following statements is correct for the crustal model given in Fig. A?
To determine which statement is correct regarding the timing of seismic wave arrivals from shallow and deep earthquakes, we need to consider the travel times of P-waves (primary waves) and S-waves (secondary waves) through the earth’s crust.
Given the information from the crustal model, we can interpret the velocity structure and find out how the depths of the earthquakes affect the travel time differences between P-waves and S-waves.
- \(V_1 = 6.0 \, \text{km/s}\), \(z_1 = 12 \, \text{km}\)
- \(V_2 = 6.5 \, \text{km/s}\), \(z_2 = 12 \, \text{km}\)
- \(V_3 = 6.8 \, \text{km/s}\), \(z_3 = 12 \, \text{km}\)
- \(V_4 = 8.0 \, \text{km/s}\), \(z_4 = 40 \, \text{km}\)
P-waves travel faster than S-waves. The travel time difference \((T_s - T_p)\) between the S-wave and P-wave arrivals is influenced by the depth of the earthquake.
- Shallow Earthquake:
- Occurs closer to the surface; hence P and S wave travel a shorter distance in the higher velocity layers.
- \((T_s - T_p)\) is larger due to longer path traveled in lower velocity layers.
- Deep Earthquake:
- Occurs deeper; thus P and S waves travel more distance in higher velocity layers.
- \((T_s - T_p)\) is smaller since waves travel more distance in faster layers.
Thus, the correct statement for this scenario is:
Ts-Tp is smaller for the deeper earthquake than the shallower earthquake.
Important Questions from Seismology
- A geophysicist travelling from the Bay of Bengal through the Ganga plain to the Himalaya, estimates the depth of Moho discontinuity. Which one of the following is the correct order of the Moho-depth estimates?
- Compressional wave velocity is the highest in
- If $V_m$, $V_o$ and $V_i$ are the average P-wave velocities in the lower mantle, outer core and inner core respectively, then
- PKS and SKP phases of a surface focus earthquake reach an observatory
- In a homogeneous isotropic medium with a free surface
