Global distribution of tectonic hazards

• Tectonic hazards include earthquakes and volcanic eruptions, as well as secondary hazards like tsunamis
• The global distribution of tectonic hazards is explained by plate boundaries and other tectonic processes
• About 70% of all earthquakes are found in the 'Ring of Fire' in the Pacific Ocean
• The most powerful earthquakes are associated with convergent or conservative boundaries
• The oceanic fracture zone (OFZ) is a belt of activity through the oceans along the mid-ocean ridges, coming ashore in Africa, the Red Sea, the Dead Sea rift and California
• The continental fracture zone (CFZ) is a belt of activity following the mountain ranges from Spain, via the Alps, to the Middle East, the Himalayas to the East Indies and then circumscribing the Pacific
• Scattered earthquakes in continental interiors can occur along old fault lines, like the Church Stretton Fault in Shropshire
• Earthquakes are primary hazards (ground movement and ground shaking) but also cause secondary hazards like landslides and tsunamis
• The violence of a volcanic eruption is determined by the amount of dissolved gases in the magma and how easily the gases can escape
• There are about 500 active volcanoes throughout the world, with around 50 of them erupting each year
• Volcano: A landform that develops around a weakness in the Earth's crust from which molten magma, volcanic rock and gases are ejected or extruded
• Plate boundaries are categorized into three types: divergent (constructive) margins, convergent (destructive) margins, and conservative (transform) margins
• Divergent margins are most clearly displayed at mid-ocean ridges, with frequent small earthquakes and new oceanic crust created
• Convergent margins involve plates moving together, causing frequent earthquakes and volcanoes due to plate material melting in the mantle
• Conservative margins involve one plate sliding against another horizontally, resulting in extensive shallow focus earthquakes but no volcanic activity
• Plates can move away from each other at divergent boundaries, slide past each other at transform boundaries, or crunch into each other at convergent boundaries
• At divergent boundaries, new oceanic crust is created, leading to frequent small earthquakes that are typically low hazard risk
• Transform boundaries, like the San Andreas Fault in California, pose more risk as plates slide past each other, creating friction and potential for earthquakes
• Convergent boundaries, where two plates move towards each other, can generate large and damaging earthquakes, tsunamis, and volcanoes due to one plate sliding under the other