Main hazards: ground-shaking, liquefaction, landslides, tsunami, aftershocks

Earthquake & Volcanic Hazards & Impacts

Ground‑Shaking ⚡️

Think of the Earth as a giant drum. When tectonic plates collide, the drumhead (the crust) vibrates, producing ground‑shaking. The intensity is measured by the Richter scale or the Moment‑Magnitude scale (Mw):

• $M_w = \frac{2}{3}\log_{10}E - 6.07$, where $E$ is the energy released.
• Strong shaking can cause buildings to sway like a pendulum and lead to structural failure.

Liquefaction 🌊

When saturated, loose soils lose strength during shaking, acting like liquid sand. Imagine pouring water into a cup of dry sand – the sand collapses. Key points:

• Occurs in water‑rich, unconsolidated soils.
• Can lift foundations, causing buildings to tilt or sink.
• Example: 1964 Niigata, Japan – many houses sank after the quake.

Landslides 🏔️

Earthquakes destabilise slopes, triggering landslides. Think of a sliding ice cube that suddenly rushes downhill. Important facts:

1. Trigger: rapid ground motion or liquefaction.
2. Impact: blocks roads, destroys habitats, and can generate secondary tsunamis.
3. Case study: 2014 Oso, Washington – a massive landslide buried a community.

Tsunami 🌊🌊

Under‑sea earthquakes displace the seafloor, pushing water like a giant water slide. Key points:

• Wave height can reach >10 m near the source.
• Travel time: 1–2 hours to reach coastlines 200 km away.
• Example: 2004 Indian Ocean tsunami – over 230,000 deaths.

Aftershocks 🔁

After the main quake, smaller tremors continue. Think of a drum that keeps beating after the first strike. Typical pattern:

1. Frequency decreases with time: $N(t) = \frac{K}{(t+c)^p}$ (Omori’s law).
2. Can damage already weakened structures.
3. Example: 2011 Tohoku, Japan – 1,000+ aftershocks in the first week.

Exam Tips 📚

Hazard Comparison Table 📊