3 Earthquake Activity Revision Summary Components of earthquakes
• Shallow focus • Intermediate focus • Deep focus • Epicentre • Seismic waves (tremor) • Fault line • Aftershock
Where earthquakes occur Convergent plate boundaries
• Oceanic plate collides with another tectonic plate – 2011 shallow megathrust earthquake 72 km off Japanese coast – Pacific Plate (oceanic) converged with and subducted under the Eurasian Plate (continental) – earthquake lead to a tsunami
• Two continental plates collide – April 2015 – 8.1 magnitude earthquake in Nepal – Indian Plate collided with and slipped under Eurasian Plate releasing a large build-up of energy
Divergent plate boundaries
• Earthquakes where two plates separate – Mid-Atlantic Ridge – movements often go unnoticed, as no lives lost and no property damaged
Transform plate margin
• San Andreas Fault in California – Pacific and North American plates slide past one another – lock in position, stress builds up – earthquakes occur when energy released – focus tends to be close to the earth’s surface
Earthquake measurement Seismograph
• Measures the intensity of seismic waves – vertically and horizontally
