Geography · Year 12 · Tectonic Processes and Hazards · Spring Term

Earthquake Hazards: Primary and Secondary

Examine the direct impacts of ground shaking and secondary hazards like tsunamis, landslides, and liquefaction.

• National Curriculum Attainment Targets
• A-Level: Geography - Tectonic Processes and Hazards
• A-Level: Geography - Hazard Management and Mitigation

About This Topic

Earthquake hazards split into primary effects from direct ground shaking, which cause structural damage, fires, and injuries at the epicenter, and secondary effects that follow, such as tsunamis from seabed displacement, landslides on unstable slopes, and liquefaction where water-saturated soils lose strength and behave like liquids. Students differentiate these by examining how primary hazards strike immediately and locally, while secondary ones amplify destruction over wider areas and longer times. For liquefaction, they explore conditions like loose, saturated sands under cyclic shaking; for tsunamis, vertical seafloor movement generates waves that grow destructive offshore.

This content aligns with A-Level Geography's Tectonic Processes and Hazards unit, building skills in hazard analysis, risk assessment, and mitigation planning. Students connect hazards to tectonic settings, like subduction zones prone to both shaking and tsunamis, preparing them for case studies on events such as the 2011 Tohoku earthquake.

Active learning benefits this topic greatly because students model processes with everyday materials, predict outcomes in groups, and debrief real data. Shaking trays reveal liquefaction dynamics, while wave simulations clarify tsunami propagation. These methods turn complex, infrequent events into observable phenomena, fostering critical analysis and retention through direct engagement.

Key Questions

1. Differentiate between primary and secondary earthquake hazards.
2. Explain the conditions necessary for liquefaction to occur and its destructive potential.
3. Analyze the formation and impact of tsunamis generated by submarine earthquakes.

Learning Objectives

• Differentiate between primary earthquake hazards, such as ground shaking and building collapse, and secondary hazards, including tsunamis, landslides, and liquefaction, by analyzing their causes and immediate effects.
• Explain the specific conditions, including loose, saturated soil and cyclic loading, required for liquefaction to occur and evaluate its destructive potential on infrastructure.
• Analyze the formation of tsunamis from submarine earthquakes, describing the role of vertical seafloor displacement and predicting their wave behavior and impact zones.
• Compare the spatial and temporal characteristics of primary and secondary earthquake hazards, assessing which pose a greater risk in different geological settings.

Before You Start

Plate Tectonics and Plate Boundaries

Why: Understanding the movement and interaction of tectonic plates is fundamental to comprehending the causes of earthquakes and their distribution.

Earthquake Waves (P, S, Surface Waves)

Why: Knowledge of seismic wave types is necessary to differentiate between the direct impact of ground shaking and subsequent secondary effects.

Key Vocabulary

Liquefaction	A phenomenon where saturated soil or sediment temporarily loses strength and acts like a liquid due to increased pore water pressure, often caused by seismic shaking.
Tsunami	A series of large ocean waves generated by a sudden displacement of a large volume of water, typically caused by underwater earthquakes, volcanic eruptions, or landslides.
Ground Shaking	The violent movement of the Earth's surface caused by seismic waves radiating from an earthquake's focus, leading to direct structural damage.
Landslide	The rapid downhill movement of rock, debris, or earth, often triggered by seismic activity on unstable slopes.
Pore Water Pressure	The pressure of groundwater held within the pores of soil or rock, which can increase during seismic shaking and lead to liquefaction.

Watch Out for These Misconceptions

Common Misconception

Secondary hazards are always less destructive than primary ones.

What to Teach Instead

Secondary hazards often cause more widespread or delayed devastation, like tsunamis traveling thousands of kilometres. Active group modeling and case study rotations help students compare scales visually, challenging assumptions through evidence from multiple events and peer debate.

Common Misconception

Liquefaction only happens in coastal areas or during major earthquakes.

What to Teach Instead

Liquefaction occurs in any saturated, loose soil under moderate shaking from distant quakes. Hands-on tray experiments with varied soils let students test conditions directly, revealing triggers beyond magnitude and location, building accurate mental models via trial and observation.

Common Misconception

All submarine earthquakes produce tsunamis.

What to Teach Instead

Only those with significant vertical displacement generate large tsunamis; horizontal slip does not. Wave simulations in pairs allow students to test fault types, observe wave formation differences, and connect to seismology data, refining predictions through structured experimentation.

Active Learning Ideas

Model Building: Liquefaction Shake

Provide trays with dry sand, wet sand, and saturated sand layers. Students shake trays at set frequencies using a simple shaker device, observe settling and flow, then measure surface displacement. Groups record variables like water content and shaking intensity, drawing links to real soil conditions.

35 min·Small Groups

Jigsaw: Hazard Impacts

Assign groups one earthquake case, like Christchurch 2011 or Sumatra 2004, focusing on primary or secondary hazards. Each expert group analyzes data on impacts and mitigation, then jigsaws to teach peers. Conclude with class timeline comparing hazard sequences.

50 min·Small Groups

Simulation Pairs: Tsunami Waves

Pairs use shallow water trays to model seabed uplift by pushing the bottom suddenly, timing wave travel and height changes with depth. Add barriers as coastlines, measure run-up, and graph results. Discuss parallels to real monitoring systems.

40 min·Pairs

Mapping Carousel: Hazard Zones

Stations feature maps of a tectonic region; students identify primary and secondary risk zones, annotating triggers and mitigation. Rotate every 10 minutes, adding peer notes. Whole class synthesizes a composite risk profile.

45 min·Small Groups

Real-World Connections

• Civil engineers in coastal cities like Tokyo and San Francisco analyze tsunami inundation maps, developed using seismic data and wave modeling, to design earthquake-resistant infrastructure and evacuation routes.
• Geotechnical engineers assess soil stability in earthquake-prone regions, such as parts of New Zealand and California, advising on construction practices to mitigate the risks of liquefaction and landslides.
• Emergency management agencies, like FEMA in the United States, use historical data on earthquake impacts, including tsunami events like the 2004 Indian Ocean tsunami, to develop response plans and public warning systems.

Assessment Ideas

Exit Ticket

Provide students with a brief description of an earthquake scenario. Ask them to identify at least two primary and two secondary hazards that could result, and briefly explain why each is classified as primary or secondary.

Discussion Prompt

Pose the question: 'Under what specific geological conditions is a submarine earthquake most likely to generate a destructive tsunami versus causing significant localized ground shaking?' Facilitate a class discussion where students use key vocabulary to explain their reasoning.

Quick Check

Present students with images or short video clips depicting different earthquake impacts (e.g., collapsed buildings, flooded coastlines, tilted structures, flowing mud). Ask them to label each as a primary or secondary hazard and provide a one-sentence justification.

Frequently Asked Questions

What differentiates primary and secondary earthquake hazards?

Primary hazards stem directly from ground shaking, causing immediate damage like collapsed buildings and injuries near the epicenter. Secondary hazards arise afterward, including tsunamis from seabed shifts, landslides on slopes, and liquefaction in wet soils. This distinction is key for A-Level risk profiling, as secondary effects often extend impacts regionally and demand specific monitoring strategies like early warning systems.

What conditions trigger earthquake-induced liquefaction?

Liquefaction requires loose, granular soils saturated with water, subjected to cyclic shaking that increases pore pressure and reduces friction. Common in river valleys or reclaimed land, it turns ground to quicksand-like state, toppling structures. Students grasp this via models showing how drainage or soil compaction mitigates risk, linking to hazard management in the curriculum.

How do submarine earthquakes generate tsunamis?

Vertical displacement of the seafloor during undersea quakes pushes water upward, creating waves that amplify over distance due to shoaling near coasts. Unlike wind waves, tsunami wavelengths span hundreds of kilometres with small open-ocean heights but devastating run-up. Analysis of events like 2004 Indian Ocean builds understanding of detection via DART buoys and evacuation planning.

How can active learning help teach earthquake hazards to Year 12 students?

Active methods like sand-tray liquefaction demos, tsunami wave tanks, and case study jigsaws make abstract processes concrete and collaborative. Students predict, test, and debrief in groups, linking models to A-Level case studies for deeper retention. This approach counters passivity in complex topics, develops analytical skills through evidence handling, and mirrors real hazard assessment teamwork.