Grade 10 Geography – Earthquakes Quiz

Most earthquakes are caused by sudden movement along faults where tectonic plates or crustal blocks slide, pull apart or collide. In Kenya the East African Rift involves crustal movement that produces earthquakes.

The focus (or hypocentre) is the underground point where fault rupture starts. The epicentre is the location on the surface directly above the focus.

The epicentre is the surface location directly above the earthquake focus; it is often where shaking is strongest at the surface.

P waves are compressional waves that travel fastest through the Earth and therefore arrive before S waves and surface waves.

Surface waves travel along the Earth’s surface and often have larger amplitudes and longer durations, causing the greatest shaking and damage.

A seismograph or seismometer detects and records ground motions produced by seismic waves and is the basic tool for measuring earthquakes.

The moment magnitude scale (Mw) is widely used because it more accurately measures large earthquakes than the older Richter scale. The Modified Mercalli scale measures intensity, not magnitude.

The Modified Mercalli scale describes observed effects and damage at different locations (intensity), unlike magnitude scales which quantify energy release.

The East African Rift is a zone where the crust is pulling apart (divergent/extension), causing normal faulting and earthquakes in Kenya.

Liquefaction occurs when shaking increases water pressure in loose saturated soils, reducing strength and causing the ground to flow and buildings to sink or tilt.

Aftershocks are smaller quakes occurring after the main event as the crust rebalances; they can still cause damage to already weakened structures.

Foreshocks are smaller quakes that precede some larger earthquakes, but not all mainshocks have identifiable foreshocks, so they are not reliable predictors.

Buildings with ductile (flexible) frames, proper reinforcement and good foundations perform better during earthquakes by absorbing and redistributing seismic forces.

Tsunamis most often result when an earthquake under the sea causes rapid uplift or subsidence of the seabed, moving the water column and generating waves.

While scientists can estimate long-term probabilities for earthquake occurrence in a region, exact short-term predictions of time and place remain beyond current capability.

The East African Rift involves tensional forces that stretch the crust, producing faults and frequent seismic activity where blocks of crust move.

The Rift Valley region in Kenya sits along the East African Rift and experiences geological faulting and related earthquakes more often than coastal islands.

Shallow quakes release energy closer to the surface, so seismic waves have less distance to travel and usually cause stronger shaking and more damage.

A fault is a crack in the crust where blocks of rock move relative to each other; earthquakes commonly occur on faults.

Changing underground pressures by injecting or removing fluids can alter stress on faults and has caused induced seismicity in some regions; natural activities like planting trees do not.

Early warning systems use sensors to detect the initial P waves and quickly transmit alerts so people and automated systems can take protective action before stronger shaking arrives.

Soft or reclaimed soils can trap and amplify seismic waves, causing stronger shaking and greater damage than areas underlain by stiff bedrock.

While building collapse, fires and landslides are immediate hazards during or right after shaking, economic disruption and job losses are longer-term consequences.

S waves are shear waves that move material side to side or up and down (perpendicular to travel) and cannot pass through liquids such as the outer core or saturated pore fluids.

The recommended safe action is to drop, cover and hold on to protect from falling objects, and being prepared with an emergency kit improves survival after the shaking stops.

The East African Rift (including the Great Rift Valley) is a divergent zone where the crust is being pulled apart (tension), producing normal faults and earthquakes.

The focus (hypocentre) is the location inside the Earth where rock first breaks and seismic energy is released; the epicentre is the point on the surface above it.

The epicentre is the surface point above the focus where the effects of the earthquake are often strongest.

Rift valleys form where the crust is stretched and thinned; this extension produces normal faults in which one block drops down relative to another.

P-waves are compressional primary waves that travel fastest through the Earth and arrive before S-waves and surface waves.

S-waves involve shear motion and cannot propagate through liquid layers such as the outer core, so they are blocked there.

Surface waves (Love and Rayleigh) travel along the Earth's surface and produce large, damaging ground motions that affect structures.

Seismologists use the time difference between P- and S-wave arrivals at three or more seismograph stations to triangulate the epicentre location.

Magnitude (e.g., moment magnitude) quantifies the total energy released by an earthquake at its source.

The moment magnitude scale (Mw) is the modern standard for measuring earthquake size because it better represents the total energy released, especially for large quakes.

Earthquake risk in Kenya is higher along the East African Rift, which affects regions including Turkana, Nakuru and other Rift Valley areas.

Aftershocks are smaller quakes that follow the mainshock as the crust adjusts to the changed stresses.

Reinforced construction with proper foundations on stable ground reduces collapse risk; unreinforced masonry and soft soils raise damage and collapse likelihood.

Liquefaction occurs during strong shaking of water-saturated sediments, reducing their strength and causing structures to settle or topple.

Dropping, taking cover under sturdy furniture, and holding on protects against falling objects and reduces the risk of injury during shaking.

Filled or loose soils can amplify seismic waves and are prone to liquefaction, increasing building damage and collapse risk.

Regular drills, securing furniture and teaching safe responses (drop, cover, hold) help reduce injuries and improve readiness.

Seismographs record ground motions caused by seismic waves and are essential for detecting and measuring earthquakes.

Magnitude is a single value representing energy release; intensity (e.g., Modified Mercalli) describes varying local effects and damage at different places.

Activities like fluid injection, mining or reservoir filling can change subsurface pressure and stress, sometimes inducing small earthquakes.

Early warning systems detect initial fast P-waves and can warn of stronger shaking seconds to minutes later, giving time to take protective actions even though they cannot prevent quakes.

In rift zones, both volcanic activity (magma movement) and tectonic extension (faulting) can generate earthquakes, sometimes related to each other.

Seismic hazard maps display the probability of ground shaking across regions and help planners and engineers design safer buildings and land use.

Reinforced concrete with properly anchored steel bars increases ductility and strength, helping structures withstand seismic forces.

An earthquake swarm is a cluster of small quakes over days to months, commonly occurring in areas with volcanic or rifting activity like the Rift Valley.

The hypocenter or focus is the point beneath the Earth's surface where fault rupture and seismic energy release begin; the epicenter is the point on the surface directly above it.

The East African Rift is a rift system where the crust is being pulled apart (divergent), causing normal faulting and earthquakes in Kenya and neighboring regions.

P-waves are compressional waves that travel fastest, arriving first and passing through both solids and liquids, unlike S-waves which cannot travel through liquids.

A seismograph or seismometer detects and records ground motion caused by seismic waves during earthquakes.

Magnitude (e.g., moment magnitude) quantifies the total energy released by an earthquake, while intensity describes shaking effects at specific places.

The Modified Mercalli Intensity scale rates the effects and damage of an earthquake at specific locations, using observable impacts rather than energy.

Undersea earthquakes that abruptly displace the seafloor vertically push water and generate tsunamis; wind and liquefaction do not directly create tsunami waves.

S-waves involve shear motion which requires a material to resist shape change; the liquid outer core cannot support shear so S-waves are not transmitted through it.

Aftershocks are smaller earthquakes occurring near the rupture area after the mainshock as the crust adjusts to the changed stress.

Liquefaction happens when shaking increases water pressure in saturated sandy soils, causing them to behave like a liquid and undermining foundations and buildings.

Dropping to the ground, taking cover under a sturdy table, and holding on protects you from falling objects and debris during shaking; running out can expose you to falling hazards.

The Rift Valley is an active rift zone where crustal extension produces earthquakes; coastal and island areas away from the rift have lower seismicity.

Base isolation systems allow a building to move independently of ground shaking, reducing energy transfer and damage; heavy decorations and loose fills increase risk.

P-waves travel fastest but are less damaging; their detection can trigger seconds to minutes of warning before the damaging waves arrive, allowing protective actions.

The moment magnitude scale better represents the total energy released, especially for very large earthquakes; the original Richter scale saturates for large events.

The epicenter is the surface location directly above the earthquake's focus (hypocenter) and is commonly plotted on maps showing earthquake locations.

Seismic belts are regions where earthquakes concentrate due to tectonic activity, such as the Pacific Ring of Fire or the East African Rift.

Changing underground fluid pressures through activities like geothermal operations or reservoir impoundment can activate faults and trigger small earthquakes.

If fault displacement extends to the surface, the ground can rupture along the fault trace, breaking roads and structures.

Foreshocks are smaller seismic events that occur before a larger mainshock in the same area, but not all mainshocks have identifiable foreshocks.

Poor construction without reinforcement, weak materials, or bad design makes buildings vulnerable to collapse when shaken, increasing injury and death.

Tectonic stretching along the Rift produces steep escarpments and down-dropped rift valley floors (grabens) characteristic of the East African Rift.

Large underwater earthquakes can generate tsunamis; coastal communities need to move to higher ground if warned, even if shaking has stopped.

Combining geological mapping, historical earthquake data and continuous seismic monitoring helps assess active faults and earthquake hazards.

Seismic gaps are segments of faults showing little recent activity despite surrounding quakes; they may indicate accumulated strain and a potential site for a future large earthquake.