Why in the News?

An 8.8 magnitude earthquake hit off Russia’s Kamchatka Peninsula, triggering 16-foot tsunamis that reached Hawaii and northern California in the US.

About Earthquakes:

Overview: Sudden ground shaking caused by release of stored energy in Earth’s crust due to tectonic stress.
Cause: Occurs when tectonic plates slip at fault lines where stress had built up due to friction.
Seismic Waves: Energy travels as:
- Primary Waves (P-waves): Fastest, compressional.
- Secondary Waves (S-waves): Slower, shear motion.
Key Terms:
- Focus (Hypocenter): Underground origin point.
- Epicenter: Surface point directly above the focus.
Measurement:
- Magnitude: Energy released (Richter Scale, logarithmic).
- Intensity: Observed ground shaking (varies by location).
- Seismograph: Records seismic wave activity.

Underwater Epicenter: Must occur beneath oceans to displace water.
Shallow Depth: Quakes at <70 km transfer energy more efficiently to water surface.
Reverse Faulting: One tectonic plate pushes over another, vertically shifting the seafloor.
Rapid Displacement: Sudden seafloor uplift/downthrust generates massive water waves.
High Magnitude: Quakes >7.0 (especially >8.0) likely to trigger tsunamis.

Overview: Russian Far East; borders the North Pacific Ocean.
Tectonic Zone: Sits on the Kuril-Kamchatka Trench—Pacific Plate subducting under Okhotsk Plate at ~86 mm/year.
Seismic Hotspot: Historical major quakes in 1841, 1923, 1952, 2006, and 2020.
Ring of Fire: Part of the 40,000 km Pacific Ring of Fire , known for quakes and volcanoes.
2025 Earthquake:
- Depth:3 km (shallow)
- Impact: Triggered tsunami waves up to 16 ft—one of the strongest earthquakes since 1900.

[UPSC 2004] Consider the following geological phenomena:

1. Development of a fault 2. Movement along a fault 3. Impact produced by a volcanic eruption 4. Folding of rocks

Which of the above cause earthquakes?

Options: (a) 1, 2 and 3 (b) 2 and 4 (c) 1, 3 and 4 (d) 1, 2, 3 and 4*