Beyond Fault Lines: 8 Hidden Earthquake Dangers

Written by Saunders Seismic on 25th February 2025

When it comes to seismic safety, it’s common to focus on fault lines as a primary cause of earthquake damage. While fault line proximity is significant, relying solely on it can leave your commercial and industrial buildings vulnerable to other unforeseen dangers.

Evaluating a range of risk factors beyond fault lines is essential to safeguarding investments and enhancing your building’s structural integrity. By doing so, you can develop a comprehensive strategy to mitigate earthquake damage, ensuring your properties’ and tenants’ safety and longevity.

This article highlights eight important critical factors that influence seismic safety, providing you with the knowledge to protect your assets and enhance your building’s resilience to seismic events:

PGA Soil and Ground Conditions
Building Design and Construction
Local Seismic Activity and Building Codes
Building Height and Mass Distribution
Proximity to Other Structures
Topography and Surrounding Environment
Infrastructure Resilience
Community Preparedness and Response Plans

1. PGA Soil and Ground Conditions

Soil type affects how a building responds to an earthquake. Higher Peak Ground Acceleration (PGA) values (above 4.2) increase construction costs due to the need for stronger structural designs. In some cases, this can more than double normal costs.

Structures built on solid rock or well-compacted soils (lower PGA) typically experience less shaking and are less likely to suffer severe damage. In contrast, buildings on soft, loose, or water-saturated soils (higher PGA) are at a greater risk. These soils can amplify seismic waves and are prone to liquefaction, particularly in sandy soils with a high water table.

Liquefaction causes the ground to temporarily behave like liquid during an earthquake. Imagine a bowl of Jell-O representing the soil – it will shake much more vigorously than a solid surface. This can cause buildings to tilt, sink, or collapse, even if they are otherwise structurally sound. Areas with high water tables, such as riverbanks and coastal zones, are especially vulnerable.

The 1971 Sylmar earthquake in California showed how unstable soil conditions lead to severe damage. In contrast, buildings in New York, constructed on granite, experience less movement. Measuring 6.6 on the Richter scale, the Sylmar quake led to building and infrastructure collapse, spurring advancements in seismic safety regulations and building codes.

Earthquake damage to VA hospital in Sylmar, February 9, 1971
Source

What Is Peak Ground Acceleration (PGA)?

PGA measures the highest rate of ground movement recorded at a location during an earthquake. It is expressed in units of g, where g represents Earth’s gravitational acceleration (9.81 m/s²). Higher PGA values indicate stronger shaking, which increases structural stress and potential damage.

PGA is a key factor in seismic design because it determines the forces acting on a building during an earthquake. Engineers use PGA values to assess site-specific risks and implement appropriate reinforcements. Areas with high PGA require stronger foundations, flexible structural connections, and advanced seismic dampening techniques to minimize damage.

2. Building Design and Construction

Buildings built before 1996 may lack proper seismic reinforcements and should have a seismic assessment at the very least. Buildings with weak structural elements, inadequate connections between components, or irregular shapes are more likely to fail during an earthquake.

Modern buildings are designed with seismic resilience in mind, employing techniques such as shear walls, base isolators, and steel bracing to withstand seismic forces. Implementing these advanced design strategies in new construction or retrofitting older buildings can greatly reduce the risk of significant damage.

3. Local Seismic Activity and Building Codes

Regions with a history of frequent or severe earthquakes but with outdated or poorly enforced building codes face higher risks. However, areas with strict, well-enforced modern building codes and low to moderate seismic activity have the lowest risk.

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“Earthquakes don’t kill people; buildings do.”
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Here is a map of hazard-resistant building code adoption across the US from FEMA.

4. Building Height and Mass Distribution

Tall buildings and structures with uneven weight distribution (e.g., heavy roofs or asymmetrical designs) face more stress during an earthquake. Whereas balanced, low-rise buildings with symmetrical mass distribution are more stable and less likely to suffer significant damage.

5. Proximity to Other Structures

Buildings close to each other can face the risk of “seismic pounding,” where adjacent structures collide during shaking, causing significant damage. This risk is higher in densely built urban areas, where buildings are often constructed with minimal spacing.

The force of seismic waves can cause buildings to sway and move. Without sufficient separation, this movement can result in severe structural impacts. Seismic pounding can lead to cracked walls, damaged support columns, and even the collapse of portions of a building.

6. Topography and Surrounding Environment

Buildings on slopes, near cliffs, or unstable land are at higher risk due to potential landslides, rockfalls, or ground settling triggered by seismic activity.
Conversely, buildings on flat, stable terrain with no significant nearby geographical hazards generally face lower risk.

Check out the latest map from the USGS National Seismic Hazard Model (2023) to see seismic hazard levels across the U.S. It includes updated earthquake data and fault-slip rates to help assess potential risks.

Local geological conditions may amplify ground motions, potentially increasing the hazard levels shown on the map.

7. Infrastructure Resilience

Surrounding infrastructure impacts seismic safety. Weak roads, bridges, and utility lines increase risks. Poorly maintained infrastructure can lead to secondary impacts, such as power outages, water main breaks, and restricted emergency access after an earthquake.

8. Community Preparedness and Response Plans

Community preparedness and response plans can influence building risk during an earthquake. Communities with well-developed and practiced emergency response plans can lessen the impact of seismic events on both buildings and inhabitants.

For example, cities like San Francisco and Los Angeles have implemented extensive earthquake preparedness programs, including public education campaigns, neighborhood emergency response teams, and annual drills such as the Great California ShakeOut.

For businesses, having an earthquake preparedness plan is critical. These plans should include:

Securing heavy equipment and sensitive materials
Establishing protocols for employee safety
Ensuring operational continuity to minimize downtime and financial losses in the aftermath of an earthquake

Saunders Seismic: Strengthening Structures. Supporting Businesses.

Seismic retrofitting is vital for enhancing existing buildings’ earthquake resistance. This proactive approach protects lives, preserves property, and ensures compliance with modern building codes and standards.

Saunders Seismic helps commercial and industrial property owners improve the safety and durability of their buildings in earthquake-prone areas by assessing structural vulnerabilities and implementing targeted reinforcement techniques. Our experienced crews handle all retrofitting work, ensuring quality and efficiency.

Concerned about the seismic safety of your buildings? Partner with Saunders Seismic to protect your real estate investments and enhance structural resilience. Our expert team specializes in comprehensive seismic assessments and retrofits tailored to your building’s unique needs – with minimal tenant disruptions. We can also provide a rough estimate of retrofit costs to help with project budgeting.