Earth Science: Earthquake Risk Maps and Building Choices
Using seismic hazard information to make safer construction decisions
Earth Science: Earthquake Risk Maps and Building Choices
Using seismic hazard information to make safer construction decisions
Earth Science - Grade 9-12
- 1
A seismic hazard map shows a city in a zone labeled high peak ground acceleration. Explain what peak ground acceleration means and why a high value matters for building design.
Think about how quickly the ground can speed up and change direction during shaking.
Peak ground acceleration is a measure of how strongly the ground is expected to shake during an earthquake. A high value matters because buildings in that area must be designed to resist stronger horizontal and vertical forces. - 2
Two towns are the same distance from an active fault. Town A is built on solid bedrock, and Town B is built on loose water-saturated sand. Which town is likely to experience more damage during the same earthquake, and why?
Consider how different ground materials respond to seismic waves.
Town B is likely to experience more damage because loose water-saturated sand can amplify shaking and may undergo liquefaction. Solid bedrock usually shakes less intensely than soft, loose sediment. - 3
A developer wants to build a hospital in a region with moderate earthquake hazard. List three building choices that would reduce earthquake risk for this hospital.
The hospital should use a reinforced structural frame, secure heavy equipment and utilities, and include flexible connections for pipes and electrical systems. It should also be built on a well-studied site with stable ground. - 4
A risk map shows a high hazard zone along a fault, but the population density there is very low. Another area has moderate hazard but very high population density. Explain why the moderate hazard area could still have higher overall earthquake risk.
Risk is not the same as hazard. Think about what is present in the danger zone.
Earthquake risk depends on both hazard and exposure. The moderate hazard area could have higher overall risk because many more people, buildings, roads, and services could be harmed during an earthquake. - 5
Use this building table: Building 1 is unreinforced brick on soft soil. Building 2 is steel frame with base isolation on bedrock. Building 3 is wood frame on firm soil. Rank the buildings from highest to lowest expected earthquake safety and explain your ranking.
The safest is Building 2 because a steel frame with base isolation on bedrock is designed to reduce shaking damage. Next is Building 3 because wood frames are lighter and flexible, and firm soil is more stable. The least safe is Building 1 because unreinforced brick is brittle and soft soil can amplify shaking. - 6
A coastal city has a high earthquake hazard and some areas are less than 10 meters above sea level. What additional earthquake-related hazard should planners consider, and what is one building or planning choice that can reduce danger?
Strong offshore earthquakes can move large amounts of seawater.
Planners should consider tsunami hazard. They can reduce danger by keeping critical buildings out of tsunami inundation zones, using elevated evacuation routes, or designing vertical evacuation structures. - 7
Explain why an earthquake risk map should be updated after scientists discover a previously unmapped fault near a growing suburb.
The risk map should be updated because a newly discovered fault changes the understanding of local seismic hazard. If the suburb is growing, more people and structures may be exposed, so building codes and land-use decisions may need to change. - 8
A city map shows three possible school sites. Site A is near a fault on bedrock, Site B is far from the fault on soft sediment, and Site C is far from the fault on bedrock. Based only on this information, which site is likely the best choice for earthquake safety, and why?
Compare both fault distance and ground material.
Site C is likely the best choice because it is far from the fault and on bedrock. Distance from the fault can reduce shaking intensity, and bedrock is less likely than soft sediment to amplify shaking. - 9
A homeowner says, "My house is only one story tall, so earthquake risk maps do not matter for me." Explain why this statement is incorrect.
The statement is incorrect because even one-story homes can be damaged by strong shaking, liquefaction, landslides, or surface rupture. Risk maps help homeowners understand local hazards and choose retrofits such as foundation bolting or bracing cripple walls. - 10
A map uses darker colors to show higher expected shaking. A proposed emergency operations center is located in the darkest zone. Explain why this location creates a special concern and suggest a better decision.
Critical facilities need to work during and after a disaster.
This location is a special concern because an emergency operations center must remain usable after an earthquake. A better decision would be to place it in a lower hazard zone if possible or build it to a higher seismic performance standard with backup power and secured equipment. - 11
Describe the difference between seismic hazard and seismic risk using an example related to building choices.
Seismic hazard is the natural chance of earthquake effects such as shaking at a location. Seismic risk is the possible loss or damage, which depends on hazard plus exposure and vulnerability. For example, a high hazard area with modern earthquake-resistant buildings may have lower risk than the same area with unreinforced masonry buildings. - 12
A city requires new apartment buildings in high hazard zones to have ductile frames. Explain what ductility is and why it helps during an earthquake.
Compare bending to snapping.
Ductility is the ability of a material or structure to bend or deform without suddenly breaking. It helps during an earthquake because a ductile frame can absorb energy and continue supporting the building during shaking. - 13
A neighborhood is located on a steep slope in a region with frequent earthquakes. What hazard should be added to the earthquake risk assessment, and what are two ways to reduce the risk?
Landslide hazard should be added to the earthquake risk assessment. Risk can be reduced by avoiding construction on unstable slopes, improving drainage, using retaining structures, or stabilizing the slope with engineering methods. - 14
A public official wants to use only past earthquake locations to decide where buildings must meet stricter codes. Explain one limitation of this approach.
A quiet fault is not always a safe fault.
One limitation is that future earthquakes may occur on faults that have not ruptured recently or have not been fully identified. Building code decisions should also use fault studies, plate boundary information, soil conditions, and probabilistic hazard models. - 15
You are advising a town council choosing between retrofitting an old unreinforced masonry library or building a new library on a soft sediment site. What information would you ask for before making a recommendation, and why?
I would ask for the seismic hazard level, soil and liquefaction studies, expected occupancy, cost of retrofit versus new construction, historical value of the old building, and whether the new building would meet modern seismic codes. This information is needed because the safer choice depends on both site hazard and building vulnerability.