Tectonic Processes and Volcanic - Seismic Activity

Question

Step-by-step solution

1. Step 1

   Focus (hypocentre) (1 mark). The focus is the point BELOW the ground where the earthquake actually originates — where stored energy is first released as the rocks slip.

2. Step 2

   Epicentre (1 mark). The epicentre is the point on the Earth's SURFACE directly ABOVE the focus. A vertical line links the two; shaking is usually most intense at the epicentre.

Question

Step-by-step solution

1. Step 1

   Active (1 mark). A volcano that has erupted recently (in recorded history) and is expected to erupt again — e.g. Kilauea (Hawaii).

2. Step 2

   Dormant (1 mark). A volcano that has NOT erupted for a long time but COULD erupt again in the future — it is "sleeping", e.g. Mount Fuji (Japan).

3. Step 3

   Extinct (1 mark). A volcano that has not erupted in recorded history and is NOT expected to erupt again — its magma supply has been cut off, e.g. Edinburgh Castle Rock.

Question

Step-by-step solution

1. Step 1

   Stress builds (1 mark). Friction locks the plates at the boundary; tectonic forces keep moving the plates, so STRESS (strain energy) builds in the rock.

2. Step 2

   Sudden slip (1 mark). When the stress exceeds the strength of the rock, the rock fractures and the plates suddenly SLIP, releasing the stored elastic energy.

3. Step 3

   Seismic waves spread (1 mark). The energy travels outward as SEISMIC WAVES from the FOCUS (the underground point of slip).

4. Step 4

   Shaking felt (1 mark). The waves reach the surface; shaking is strongest at the EPICENTRE (the point directly above the focus) and weakens with distance.

Question

Step-by-step solution

1. Step 1

   Shield — shape (1 mark). GENTLE slopes and a broad base, because runny low-viscosity BASALTIC lava flows long distances before solidifying (e.g. Mauna Loa, Hawaii).

2. Step 2

   Shield — eruption (1 mark). Generally NON-EXPLOSIVE / effusive; gases escape easily from the runny lava, so eruptions are gentle.

3. Step 3

   Composite — shape (1 mark). STEEP-sided and conical, built from ALTERNATING layers of sticky ANDESITIC lava and ash (e.g. Mount Fuji, Japan).

4. Step 4

   Composite — eruption (1 mark). Highly EXPLOSIVE; viscous lava traps gas, which builds pressure until it is released violently, ejecting ash and pyroclastic flows.

Question

Step-by-step solution

1. Step 1

   Constructive / divergent. Plates move APART; magma rises (decompression melting of the mantle) to fill the gap and erupts as runny basalt. Produces mid-ocean ridges and shield volcanoes plus shallow, low-magnitude earthquakes (e.g. Mid-Atlantic Ridge / Iceland).

2. Step 2

   Destructive / convergent (subduction). A denser OCEANIC plate SUBDUCTS beneath a continental plate into the mantle. Friction and water lower the melting point, generating sticky andesitic magma → explosive composite volcanoes; the locking and slipping of the subducting slab causes powerful, often deep earthquakes (e.g. the Andes / Nazca beneath South American plate).

3. Step 3

   Conservative / transform. Plates SLIDE PAST each other. No crust is created or destroyed, so there is NO volcanic activity, but friction makes the plates lock and then jerk free, releasing large earthquakes (e.g. San Andreas Fault, California).

4. Step 4

   Collision. Two CONTINENTAL plates meet; both are too buoyant to subduct, so the crust crumples and is uplifted into fold mountains, with earthquakes but little volcanism (e.g. India colliding with Eurasia forming the Himalayas).

Question

Step-by-step solution

1. Step 1

   Magnitude — what it measures (1 mark). Magnitude is a measure of the ENERGY released at the focus of the earthquake. It is a single value for the whole event.

2. Step 2

   Magnitude — how assessed (1 mark). It is measured by instruments (seismometers) using the Richter scale or, more usually now, the moment magnitude scale. Both are LOGARITHMIC, so each whole number up represents roughly 10× greater ground shaking and about 30× more energy.

3. Step 3

   Intensity — what it measures (1 mark). Intensity describes the EFFECTS / amount of damage and shaking felt at a particular PLACE on the surface.

4. Step 4

   Intensity — how assessed (1 mark). It is judged from observed damage and people's experiences (e.g. the Modified Mercalli scale), so it VARIES from place to place for the same earthquake.

5. Step 5

   Key contrast (1 mark). One earthquake has ONE magnitude but MANY intensity values — intensity decreases with distance from the epicentre and depends on geology and building quality.