Geophysics for home safety: 6 essential tips every homeowner needs to know

Unfavorable geophysical site conditions can manifest as issues that can affect the structural integrity of your home or property. By harnessing the latest geophysical techniques, you can proactively assess your home’s vulnerability to natural disasters and structural issues without invasive, messy geotechnical drilling or guesswork. Geophysical methods are non-invasive and non-destructive; therefore, they act like X-ray vision technology that allows you to see through the soil layers without drilling, trenching, or digging.

In this guide, we’ll reveal six essential geophysics-based tips every homeowner needs to know to safeguard their sanctuary. Get ready to discover how the most versatile near-surface geophysical methods – seismic surveys, ground-penetrating radar (GPR), and electrical resistivity imaging (ERI) – can help you make informed decisions about home safety, repairs, and investments. Other geophysical techniques used less frequently in an urban setting include gravity, magnetics, and electromagnetics. Gravity surveys are expensive and slow but can produce good results in an urban setting. On the other hand, magnetics and electromagnetics are very susceptible to urban cultural noise and hardly yield trustworthy results.

Don’t wait until disaster strikes. Arm yourself with the knowledge and tools to protect your most valuable asset—your home or future property.

1. Geophysical hazards: Know the potential risks to your home

Summary:

• Risk is defined as the complex combination of three main factors: the value of the asset (house), the site hazards, and the vulnerability of the building. Each factor has its own variables.
• Geophysical hazards are hazards originating from solid earth. They are often used interchangeably with geological hazards.
• Geophysical hazards have a geophysical expression or signature and can cause significant damage to homes and pose financial and safety risks.
• Common geophysical hazards include earthquakes, volcanic activity, mass wasting (slope processes, landslides, subsidence), flooding, and coastal processes.
• Identifying and mitigating geophysical hazards is crucial for protecting your home and family.

Five types of geophysical hazards and their effects

We discuss five different types of geophysical hazards: earthquakes, volcanic activity, mass wasting (slope processes, landslides, subsidence), flooding, and coastal activity. Each type has its environmental effects.

1. Earthquakes have a variety of destructive effects. Effects caused directly by fault movement include ground shaking (and its impact on people and structures), surface rupture, landslides, fire, soil liquefaction, and regional land elevation or displacement changes.
2. Volcanic hazards include the primary effects of volcanic activity, which are the direct result of the volcanic eruption, and secondary effects, which the primary effects might cause. The primary effects include lava flows, pyroclastic activity (ash fall, ash flows, and lateral blasts), and the release of gases. The secondary effects include debris flow, mudflows, landslides, floods, and fires.
3. Mass wasting can occur in landslides, slope processes, slope stability, and subsidence. Landslides might occur with or without human activity and might cause substantial damage and loss of life. Most subsidence is induced by the natural collapse of surface and near-surface soil and rocks over underground voids or by the intentional withdrawal of fluids from subsurface reservoirs such as aquifers, hydrocarbons, and geothermal waters.
4. Flooding is a function of the total amount and distribution of precipitation in the drainage basin, the rate at which precipitation infiltrates the rock or soil, and topography. The primary effects of flooding are caused directly by the flood, including injury and loss of life and damage caused by swift currents, debris, and sediment to property and infrastructure. The secondary effects of flooding are those caused by disruption and malfunctioning of services and systems due to the flood, as well as short-term pollution of rivers, hunger and disease, and displacement of persons who have lost their homes.
5. Coastal activity manifests in coastal erosion, tropical cyclones, and tsunamis. Coastal erosion continues to produce considerable property damage that requires human intervention. Tropical cyclones claim many lives and cause vast amounts of property damage. Tsunamis are particularly hazardous along the Pacific coastlines.

Understanding the impact of geophysical hazards on residential properties

Geophysical hazards like earthquakes, volcanic activity, mass wasting, flooding, and coastal activity can devastate residential properties. These events can cause structural damage, rendering homes unsafe, expensive to repair, or uninhabitable. In extreme cases, geophysical hazards can destroy properties, resulting in significant financial losses for homeowners of future land development plans.

Moreover, geophysical hazards pose serious safety risks to families residing in affected homes. Structural damage caused by these events can create hazardous living conditions, exposing occupants to the risk of injury or death. For example, structures can collapse, and foundations or walls can crack and eventually deteriorate.

The Financial Burden of Geophysical Hazards

The financial impact of geophysical hazards on homeowners can be substantial. According to a report by the National Institute of Building Sciences, the average cost of damage caused by earthquakes alone in the United States is estimated to be $14.7 billion annually. This figure does not include the costs associated with other geophysical hazards like landslides, sinkholes, and subsidence, which can also result in significant expenses for homeowners. Naturally, home builders and land developers face the same issue.

Identifying and mitigating potential geophysical hazards is crucial for protecting your home and family from physical and financial harm. By understanding the risks associated with geophysical hazards and taking proactive steps to address them, homeowners can safeguard their properties and ensure the safety of their loved ones. Identifying, mitigating, and managing geophysical hazards is a complex but essential task for a municipality as much as for the homeowner. Effective methods to reduce geophysical hazards include land-use planning, early warning systems, ecosystem-based approaches, international cooperation, public awareness, and structural measures, of which the last two are at the homeowner level.

Common Geophysical Hazards to Watch Out For

Several geophysical hazards can affect residential properties, each with unique characteristics and potential for damage. Some of the most common hazards that silently strike include:

1. Earthquakes: Seismic events can cause ground shaking, ground rupture, soil liquefaction, trigger landslides, and mass wasting, leading to structural damage or collapse.
2. Soil liquefaction: A phenomenon in which saturated soil loses its strength and behaves like a liquid during an earthquake, causing buildings to sink or tilt.
3. Landslides: The movement of soil, rock, or debris down a slope due to gravity, often triggered by heavy rainfall, earthquakes, or human activities.
4. Subsidence: The sudden formation of a depression or hole in the ground caused by the collapse of underground cavities, often due to the dissolution of carbonate rocks or the presence of abandoned mines.
5. Coastal erosion: Although a natural process rather than a natural hazard, erosion problems occur when structures are built in the coastal zone, where ocean waves and sediment move naturally.
6. Problematic soils: Problematic soils are a group of soil materials prohibiting a building or structure’s design and construction process. They can expand, collapse, disperse, undergo excessive settlement, or even fail under relatively low-stress conditions.

Regional variations in geophysical hazards

The prevalence and severity of geophysical hazards can vary greatly depending on an area’s location and geological characteristics. For example, the United States West Coast is known for its high seismic activity due to significant active fault lines, such as fault segments of the San Andreas Fault System. In contrast, states like Florida and Texas are more prone to sinkholes due to their unique geophysical makeup, which includes extensive limestone deposits with significant karstic features.

Understanding the specific geophysical hazards that are most likely to affect your region is essential for accurately assessing the risks to your home or property and taking appropriate mitigation measures. By familiarizing yourself with your area’s geological characteristics and staying informed about local hazard types and risk assessments, you can better prepare your home and family for potential geophysical events.

Why geophysics matters for home safety

Geophysics plays a crucial role in understanding and mitigating the risks of natural hazards to residential properties. By studying the Earth’s physical properties, internal processes, and subsurface characteristics, geophysicists, geologists, and engineers can identify potential hazards, assess their likelihood and severity, and develop strategies for minimizing their impact on homes and communities.

For example, sinkholes occur in certain types of rocks in the United States, and geoscientific information has been compiled into a map that shows karst areas of the continental United States having sinkholes in soluble rocks (carbonates and evaporites), as well as insoluble volcanic rocks that contain sinkholes. The volcanic bedrock areas contain lava tubes that are voids left behind by the subsurface flow of lava rather than from the dissolution of the bedrock.  Hot spots of sinkhole activity are also shown in areas of greater susceptibility.

The importance of geophysical data for risk assessment

Geophysical data, such as seismic recordings, ground-penetrating radar (GPR) scans, and electrical resistivity images (ERI), provide valuable insights into the underlying structure and dynamics of the Earth’s subsurface. This information is essential for accurately assessing the risk of geophysical hazards in a given area and developing appropriate mitigation measures. These near-surface geophysical techniques provide a 2D or 3D image of the subsurface conditions.

For example, based on geophysical data and modeling, seismic hazard maps help identify areas most prone to earthquakes and guide building codes and construction practices to ensure homes are built to withstand seismic events. Similarly, GPR and ERI surveys can detect the presence of underground cavities or unstable soil conditions that may lead to subsidence or landslides, allowing homeowners to take preventive measures to protect their properties.

2. Home Safety Assessment: Evaluating Your Property’s Vulnerability

Summary:

• Qualified geotechnical engineers can do a geotechnical forensic study. 
• Home safety assessments can help identify potential geophysical hazards and vulnerabilities.
• Proactive assessments prevent costly repairs and ensure family well-being.
• Non-invasive geophysical methods provide data that help understand and evaluate risk levels.

The importance of conducting a home safety assessment

Conducting a home safety assessment is crucial in identifying potential geophysical hazards and vulnerabilities that may impact your property. By proactively assessing your home’s safety, you can prevent costly repairs and ensure the well-being of your family. Non-invasive, non-destructive geophysical methods, such as ground-penetrating radar (GPR) and electrical resistivity imaging (ERI), can evaluate a property’s risk level without requiring invasive techniques like drilling or excavation.

A comprehensive home safety assessment explains your property’s susceptibility to geophysical hazards, such as subsidence, sinkholes, landslides, and seismic activity. This knowledge empowers homeowners to make informed decisions about necessary repairs, upgrades, or preventive measures. You can avoid more severe and expensive problems by addressing potential issues early on. 

For example, a homeowner in the Austin, Texas, area saw a soil depression in his front garden. His first thoughts were, “It must be a cave under our home, and the soil above could sink in or collapse.” Our 3D ERI survey surveyed the garden area and a portion of the street. Luckily, the 3D ERI survey results did not find evidence of a shallow cave or sinkhole. No further geotechnical drill or excavation was required. The conclusion was that the garden’s topsoil and grass were settling a few inches. The image below illustrates this 3D ERI deployment and results.

Critical elements of a comprehensive home safety assessment

A thorough home safety assessment consists of several essential components, each contributing to a holistic understanding of your property’s vulnerability to geophysical hazards:

1. Geological desktop study: This study comprises a preliminary review of readily available and accessible geological information about your home’s location to help determine what additional data may be needed. A licensed professional geologist can do it. The geological and geophysical subsurface conditions are site-specific, which might explain why your neighbor may have a different risk than yours.
2. Foundation inspection: A qualified professional or engineer should inspect your home’s foundation. This detailed examination of the foundation conditions can reveal signs of settling, cracking, sinking, or other structural issues that may indicate underlying and undetected geological engineering problems. 
3. Soil analysis: Evaluating the composition, type, strength, and stability of the soil beneath your property can help identify potential risks, such as ‘problematic soils’ (e.g., expansive soils) or areas prone to erosion or differential settling.
4. Structural integrity evaluation: A licensed professional structural engineer can assess your home’s overall structural integrity, including the condition of essential elements like the foundation, walls, floor, roof, and windows. The evaluation can highlight weaknesses or damage that may compromise safety and structural integrity.
5. Geophysical surveys: Noninvasive geophysical methods, such as GPR, ERI, and various seismic techniques, can provide detailed images of subsurface conditions, revealing hidden hazards like sinkholes, underground voids, subsidence, problematic soils, fracture zones, faulting, shifting soil layers, or even broken buried utility lines. A professional geophysicist can perform these surveys.
6. Professional expertise: A team of experienced professionals, including geophysicists, structural engineers, geotechnical engineers, and geologists, might work independently, interpret the data collected during the assessment, and provide recommendations for addressing any identified risks.
   

The role of geophysicists in home safety assessments

Geophysical data plays a crucial role in home safety assessments because it allows for gathering information about the subsurface conditions beneath your home’s foundation or within it; GPR, ERI, or some seismic method may be handy. An experienced geophysicist later processes, analyzes, and interprets the geophysical data. By examining the acquired field data regarding seismic activity, soil composition, shallow karstic features, and other geophysical factors, the geophysicist can identify potential hazards and provide valuable insights into the subsurface conditions beneath your home.

By evaluating your home’s vulnerability to geophysical hazards, you can identify potential risks and take proactive measures to address them. For instance, geophysical imaging can investigate the occurrence of underground voids under your home’s slab that might be causing cracking of the foundation and structural walls. A homeowner in central Texas wanted to investigate whether the soil under his home’s foundation was expansive or if it had any undetected voids. The results? A 3D ERI survey did not find evidence of voids or problematic soils under the slab. If you are considering purchasing land to build on your lot, you should consider doing a subsurface site characterization with geophysics. This example (video) shows the 3D ERI method used to look for underground voids before constructing a building. However, assessing your home’s structural integrity is equally important in maintaining a safe and secure living environment.

In the next section, we will delve deeper into structural integrity and explore how homeowners can use geophysical imaging to evaluate the stability of their home’s foundation, walls, and roof. By understanding the importance of structural integrity and learning how to identify potential issues, you can take the necessary steps to safeguard your home and ensure the well-being of your family.

3. Structural integrity: Ensuring your home’s stability

Summary:

• Nondestructive geophysical methods like seismic refraction tomography (SRT), ground-penetrating radar (GRP), and electrical resistivity imaging (ERI) can assist in assessing a home’s structural integrity without invasive drilling.
• Geophysical images can reveal subsurface anomalies that help identify potential soil instabilities or areas of concern in a home’s foundation and structure.
• Preventive maintenance, targeted repairs, reinforcements, and stabilization techniques can address common structural issues detected through geophysical surveys.

The role of geophysics in evaluating structural integrity

Subsurface conditions cause many problems if they are not adequately evaluated, characterized, and, in some cases, mitigated. The onsite subsurface conditions often dictate the foundation design and construction. Hence, a foundation system needs to be appropriately designed to account for the unique soil conditions of the site, which can lead to a distressed house or building and associated claims or litigation. Nondestructive testing with 2D or 3D geophysical imaging methods (e.g., SRT, GPR, ERI) aids in the evaluation and characterization phases of the site.

Geophysical methods play a crucial role in assessing the structural integrity of a home. Techniques like GPR, SRT, and ERI measure different physical properties of the soil and rock under and around a house that give clues to finding the location, depth, and extent of problematic, weak, or unstable soil or rock mass, providing valuable insights into the condition of a home’s foundation and structure and where to focus a repair without the need for invasive, messy, and costly drilling or excavation.

2D or 3D GPR uses high-frequency radio waves to create a detailed image of the underground soils and subsurface features, including foundation cracks and voids or underground leak detection. The example below is a 3D GPR survey inside a building’s room where an underground pipe leak was suspected and successfully detected. In this example, the photographs of the investigation area within the room are delineated with blue tape (A). An annotated depth slice from 33 inches below the surface is shown in (B). Annotated GPR radargrams showed the leaking pipes and detected GPR anomalies (C to E).

SRT involves measuring the velocity of seismic body waves as they travel through the ground. The SRT method maps seismic velocity variations, from which one infers variations in soil and bedrock density, strength, and indications of fracture zones and subsurface voids that might put the home’s foundation at risk. 

ERI measures the ground’s electrical resistivity, indicating the presence of moisture, clay, sand, or gravel, subsidence spots, underground fractures and voids, and depth to bedrock, among other factors that may impact structural stability. 

A defective house’s foundation or walls are sometimes linked to undetected poor subsurface soil conditions. So, mapping the subsurface site conditions in 3D under the house is the best way to locate the issue. By using these noninvasive geophysical techniques, homeowners can gain a comprehensive understanding of their home’s structural integrity. This approach saves time and money while providing valuable data to guide any necessary repairs or reinforcements. For example, in Italy, a 3D ERI survey was done around a house to control the injection of expanding resins to treat and stabilize foundation soils.

Advantages of geophysical methods over traditional drilling

Traditional drilling methods for foundation investigation can be time-consuming, challenging to schedule, expensive, difficult to accomplish due to space and access limitations, and disruptive to the surrounding landscape. However, they directly provide a sample of the subsurface materials (soil, sediments, or rock). In contrast, geophysical methods offer several advantages:

1. Non-invasive: ground geophysical surveys do not require drilling or excavation, minimizing damage to the property and preserving landscaping.
2. Cost-effective: Geophysical methods are often more affordable than extensive drilling programs, especially when investigating large areas.
3. Comprehensive coverage: Geophysical surveys can provide continuous data (image) over a wide area, offering a better picture of subsurface conditions than isolated, single-spot drill holes.
4. When combined with minimum geotechnical drilling, the geophysical image is calibrated against one or more available soil boring logs, limiting the number of drill holes.

By leveraging the power of geophysical methods, homeowners can efficiently and effectively evaluate their home’s structural integrity without the drawbacks associated with traditional drilling. However, a drill hole may be drilled to corroborate the geophysical interpretation.

Addressing structural issues identified by geophysical surveys

Cracks or fissures are a common visible feature that you might see in a defective house or building, likely due to deleterious soil and foundation movement or settlement. Cracks or fractures may be visible in concrete walls, drywall, hard tile, exterior brick veneer, stone masonry veneer, concrete driveway, and windows and doors. Geophysical surveys (GPR, SRT, and ERI) can map the cracks or fracture zones and detect the poor subsurface soil directly below the observed structural issues that may compromise a home’s stability. Some common problems include:

1. Foundation cracks: Cracks in the foundation can allow moisture intrusion and weaken the structure over time.
2. Soil instability: Loose, poorly compacted, or expansive soils can cause uneven settling, damage to the foundation, or doors that do not close properly. Expansive soils go through cycles of expansion and contraction. Dissolution sinkholes and voids can develop underground and no longer hold the overlying weight due to a decreased soil-bearing capacity, eventually causing foundation collapse.
3. Compromised load-bearing walls: Walls weakened by weak foundation soils, water damage, termite infestation, or other factors may no longer provide adequate support for the home.

When these issues are identified through 2D, 3D, or time-lapse geophysical surveys, it’s essential to develop a targeted remediation plan design by your structural engineer of choice. The plan may involve foundation repairs, such as crack injection or underpinning, soil stabilization techniques like compaction or chemical grouting, and structural reinforcements for compromised walls.

Consulting with experienced structural engineers and geophysicists is crucial in developing an effective remediation strategy. First, the geophysicists should investigate the subsurface conditions, not the house’s structural integrity, which the structural engineer does. Second, the structural engineer should see the results and recommendations of the geophysical report before designing an action plan. These professionals can interpret the geophysical data, assess the severity of the issues, and recommend the most appropriate course of action to ensure the home’s long-term stability. 

By addressing structural issues promptly and effectively, homeowners can protect their investments, maintain property value, and provide a safe living environment for their families.

Monitoring structural health over time

Ensuring a home’s structural integrity is not a one-time event but an ongoing process. Regular geophysical monitoring can help detect changes in the foundation or structure over time, allowing for early intervention and prevention of more severe damage. GPR, SRT, and ERI are excellent choices for scanning the subsurface conditions under and around the home. Because the GPR method is fast, can adapt to small spaces, and is nondestructive, it has proven to be an excellent method for scanning the interior and exterior faces of walls, concrete slabs, driveways, sidewalks, roads, and even architectural timber beams in-situ.

Homeowners can work with geophysical service providers to establish a monitoring schedule that fits their needs and budget. Depending on the home’s age, the severity of any previously identified issues, and the in-situ geological conditions, this may involve annual or bi-annual geophysical surveys. Below is an example of a 3D ERI survey around a house. The results of the survey did not find evidence of soil instability. By proactively monitoring the home’s structural health, homeowners can stay ahead of potential problems, minimize repair costs, and maintain peace of mind, knowing that their home is stable and secure.

4. Natural disaster preparedness: safeguarding your home and family

Summary:

• Understand the natural disaster risks in your area
• Implement geophysics-based mitigation strategies to protect your home
• Stay informed and prepared with an emergency response plan

Understanding the Risk of Natural Disasters in Your Area

Natural disasters can pose significant threats to residential properties. Earthquakes, volcanic activity, mass wasting, problematic soils, hurricanes, and floods are just a few examples of the hazards that homeowners may face. The first step in safeguarding your home and family is to understand the specific risks in your area. The best way to do this is to obtain your city’s hazard mitigation plan. Almost every city in the United States has a hazard mitigation plan available for download.

Geophysical data and historical records can provide valuable insights into natural disasters’ likelihood and potential severity in a specific location. By studying past events and analyzing the geophysical characteristics of your region, you can better assess the risks your home may face.

Staying informed about local natural disaster risks and emergency response plans is crucial. Regularly check with local government agencies and trusted news sources for updates on potential threats and recommended precautions. According to the United States Geological Survey (USGS), there were 2,648 earthquakes in the United States alone from 2022 to 2023, highlighting the importance of being prepared for natural disasters. 

Sinkholes are another problem. The USGS states that there is no database of sinkhole collapses in the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved. According to the USGS, sinkhole damage over the last 15 years has cost, on average, at least $300 million annually in the United States. Since there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost. The map below shows sinkhole-prone areas in the United States.

Implementing geophysics-based mitigation strategies

Once you clearly understand the natural disaster risks in your area, it’s time to take action. Geophysics-based mitigation strategies can significantly alert you and reduce the impact of natural disasters on your home. A geophysical survey can be done when you see signs of foundation cracking, soil instability (e.g., subsidence, caving, soil expansion, erosion), or compromised load-bearing walls.

Seismic Retrofitting

In earthquake-prone regions, seismic retrofitting is crucial in protecting your home. This process involves strengthening the structural elements of your house to withstand the forces of an earthquake better. Some standard seismic retrofitting techniques include:

• Bolting the house to the foundation
• Installing shear walls to reinforce the structure
• Adding anchor bolts and steel plates to strengthen connections

Consulting with a local structural engineer is recommended to determine the most appropriate seismic retrofitting measures for your home.

Slope Stabilization

If your home is on or near a hillside, slope stabilization is essential to prevent landslides and erosion during heavy rains or earthquakes. Some effective slope stabilization methods include:

• Installing retaining walls to support the soil
• Using geotextiles to reinforce the slope
• Planting vegetation with deep root systems to hold the soil in place (it helps against soil erosion)

It is advised to work with a geotechnical engineer to assess the stability of the slopes around your home and design a customized stabilization plan. Upon completion of the slope stability work, a follow-up geophysical survey can be done to determine if the subsurface conditions have improved. However, the best piece of mind is when a geophysical survey is done ‘before and after’ the slope stability work.

5. The importance of geophysics in home safety

Summary:

• Growing demand for geophysics expertise in the housing industry.
• Homeowners benefit from working with geophysics experts.
• Geophysics identifies and helps mitigate potential hazards in homes.

How geophysics contributes to safer homes and communities

Geophysics is vital in ensuring residential properties’ safety and structural integrity. By employing various geophysical methods, professionals can identify, assess, and enhance the mitigation of potential hazards that may go unnoticed. These hazards can include unstable soil conditions, hidden faults, and groundwater issues, posing significant risks to homes and their occupants.

The insights gained from geophysical surveys and analyses provide invaluable information to homeowners, engineers, and policymakers. This data allows them to make informed decisions about home safety, land-use planning, and disaster preparedness. For example, geophysical data can help determine the most suitable locations for new housing developments, ensuring they are built on stable ground and away from potential hazards.

By applying geophysics to home safety, communities can significantly reduce the risk of disaster-related casualties and economic losses. When homes are built with a thorough understanding of the underlying geophysical conditions, they can be better built and equipped to withstand natural disasters such as earthquakes, sinkholes, landslides, and floods. This conscious approach can save lives and minimize the financial burden on homeowners, insurance companies, and governments in the aftermath of such events.

The growing demand for geophysics expertise in the housing industry

As the importance of geophysics in ensuring home safety becomes increasingly recognized, there is an increasing demand for geophysicists and related professionals in the housing industry. This demand spans various sectors, including construction, real estate, and insurance.

Geophysics in the Construction Sector

In the construction sector, geophysicists work closely with engineers and architects to ensure that new homes are built on stable ground and designed to withstand potential hazards. By conducting thorough geophysical surveys before construction begins, these professionals can identify any underlying issues that may pose risks to the home’s future occupants. This information then guides the design and construction process, ensuring the house is built to the highest safety standards. Subsurface scanning for construction site investigation is done effectively with geophysical imaging; click here to see how.

Geophysics in the Real Estate and Insurance Sectors

In the real estate sector, geophysical assessments are becoming increasingly important in the due diligence process when buying or selling a home. By providing detailed information about the geophysical conditions of a property, these assessments help buyers make informed decisions and protect their investments. 3D subsurface investigation for the real estate industry is the way to go. Similarly, insurance companies increasingly rely on geophysical data to assess the risk of insuring a particular property. This information helps insurers set appropriate premiums and ensures that homeowners have adequate coverage in the event of a disaster.

How homeowners can benefit from working with geophysics experts

Homeowners can significantly benefit from working with geophysics experts to assess and optimize their properties’ safety and resilience. By engaging the services of a qualified geophysicist, homeowners can gain a thorough understanding of their property’s geophysical subsurface conditions and potential hazards. Geophysical subsurface imaging can reveal shallowly buried hazards that may compromise the home’s foundation.

Identifying and mitigating potential hazards

Geophysics experts can conduct detailed property surveys using ground-penetrating radar (GPR), electrical resistivity imaging (ERI), and seismic techniques, which can be applied before, during, or after a home’s construction. These surveys can reveal hazards such as unstable soil conditions, underground voids, leaking utility lines, and potential landslide risks. With this information, homeowners can take proactive steps to mitigate these hazards, such as reinforcing foundations, installing drainage systems, or even relocating their homes to a safer location. In the example below, we conducted a 3D ERI survey to look for caverns that could pose a problem for future home building. We detected the possible presence of two large voids immediately below the surface, and thus, we suggested the landowner relocate the house’s footprint to an immediate safe area.

Ensuring compliance with building codes and regulations

Working with geophysics experts can help homeowners ensure that their property complies with local building codes and regulations. Geophysical assessments are required in many areas as part of the building permit process, particularly in regions prone to natural disasters. By engaging a geophysicist early in the process, homeowners can avoid costly delays and ensure their home is built to the required safety standards. These rules also apply to commercial zoning projects.

6. Geophysical methods used in home safety assessments

Summary:

• Seismic, ground-penetrating radar (GPR), and electrical resistivity imaging (ERI) surveys provide fast and detailed subsurface information.
• GPR also provides detailed scans of the building’s vertical and horizontal surfaces, such as walls and foundation concrete slabs.
• Non-invasive geophysical techniques map structures, detect underground hazards and assess soil conditions.
• Geophysical methods offer efficient, high-resolution data for comprehensive home safety assessments.

Seismic refraction and reflection surveys

Seismic refraction and reflection surveys are powerful tools in the geophysicist’s arsenal for assessing home safety. These methods utilize sound waves to create detailed images of subsurface geophysical structures, providing valuable insights into potential hazards that may lurk beneath the surface.

How seismic surveys work

In a seismic survey, a controlled source (e.g., a sledgehammer, mechanical hammer, weight drop,  or explosive charge) generates sound waves that travel through the ground. As these waves encounter different geological layers, they are refracted and reflected to the surface, where sensors, called geophones, record them. Geophysicists can construct detailed cross-sectional images of the subsurface by measuring these returning waves’ travel times and velocities.

Applications in Home Safety assessments

Seismic surveys help evaluate foundation stability, soil composition, and earthquake risk. By mapping the depth and orientation of bedrock and the thickness and properties of overlying soil layers, these surveys can identify potential weaknesses or anomalies that could compromise a home’s structural integrity.

For example, seismic data can reveal the presence of compressible or expansive soils, which can cause differential settlement and foundation damage. Additionally, seismic surveys can detect faults, fractures, voids, and other geophysical features that may amplify or dissipate seismic waves during an earthquake, helping homeowners assess their property’s vulnerability to seismic hazards.

The example below is from an undeveloped lot located in limestone terrain in Lago Vista, Texas. The terrain is prone to underground voids, sinkholes, and weak soil conditions that are unsuitable for residential construction. A shallow 2D seismic refraction tomography (SRT) coupled with an electrical resistivity imaging (ERI) survey and one geotechnical drill hole determined that the soil conditions were safe and stable for constructing a home foundation in a step-like pattern.

Advantages of seismic methods

One critical advantage of seismic surveys is their ability to cover large areas efficiently and inaccessible areas to drilling rigs. Geophysicists can quickly acquire data over extensive properties or neighborhoods by deploying multiple sensors (geophones) along a survey line or a grid. Moreover, seismic methods provide high-resolution subsurface images, allowing for detailed subsurface characterization of geological structures and potential hazards.

Ground-penetrating radar (GPR)

Ground-penetrating radar (GPR) is another essential tool in the geophysicist’s home safety assessment toolkit. This non-invasive method uses high-frequency radio waves to create detailed images of subsurface features and anomalies. It provides a 2D or 3D scan of the surfaces.

The basics of GPR

In a GPR survey, a transmitting antenna emits short pulses of high-frequency radio waves into the ground. As these waves encounter subsurface features with different electrical properties (e.g., soil layers, rocks, voids, or utilities), a portion of the energy is reflected to a receiving antenna. GPR systems can generate detailed 2D or 3D subsurface images by measuring these reflections’ travel times and amplitudes.

GPR Applications in Home Safety

GPR is handy for detecting foundation cracks, voids, underground storage tanks (UST), underground utilities, utility lines, soil thickness, and depth to bedrock, among other targets, that can impact home safety. By identifying these issues early, homeowners can proactively repair or mitigate potential hazards before they escalate into more severe problems.

For instance, GPR can locate and map UST, septic systems, and drainage pipes that may leak or fail, causing soil contamination or foundation damage. Additionally, GPR can detect voids or cavities beneath a home’s foundation, which may result from soil erosion, poor compaction, or karst activity. The image below shows an example of a 3D GPR survey that detected a UST and ruled out the existence of a UST drainage pipeline running into the adjacent lot.

Benefits of GPR

GPR’s main benefits are that it is fast, noninvasive, and provides real-time insights. Unlike destructive testing methods, GPR allows geophysicists to investigate the subsurface without disturbing the ground or damaging property. This quality makes GPR an ideal tool for assessing home safety in developed areas or landscapes where excavation is not feasible. It also aids in indicating where and how deep to target an excavation.

Moreover, GPR offers high-resolution imaging capabilities, with some systems able to resolve features as small as a few centimeters. This level of detail is crucial for identifying subtle anomalies or defects that may compromise a home’s structural integrity.

Electrical resistivity imaging (ERI)

Electrical resistivity imaging (ERI) is a powerful geophysical method that measures the electrical resistivity of subsurface materials to create detailed 2D or 3D models of the underground environment.

ERI Fundamentals

In an ERI survey, an array of electrodes is placed on the ground surface, and an electrical current is injected into the subsurface. As this current flows through the ground, it encounters materials with varying resistivity (e.g., soil, rock, water, or air-filled voids), which affects the measured voltage between the electrodes. By repeating this process for different electrode configurations and spacings, ERI systems can build up a detailed resistivity profile of the subsurface, like the example shown below.

ERI used for Home Safety assessments

ERI is particularly useful for identifying soil layers, groundwater conditions, and potential geohazards impacting home safety. By mapping the electrical resistivity distribution in the subsurface, ERI can detect variations in soil moisture, soil versus rock, fracture zones, voids, subsidence, and sinkholes, influencing foundation stability and drainage patterns.

For example, ERI can identify areas of high soil moisture or perched water tables, which may lead to foundation settlement, basement flooding, or mold growth. Additionally, ERI can detect subsurface voids, sinkholes, or other karst features that can pose significant risks to home safety and structural integrity.

Advantages of ERI

One critical advantage of ERI is its sensitivity to changes in soil moisture and material (soil/rock) composition in a 2D or 3D manner, which data can be quickly acquired. The ERI method is ideal for assessing the impact of seasonal variations, groundwater fluctuations, or land-use changes on home safety.

Moreover, ERI can provide high-resolution images of the subsurface, with some systems capable of resolving features down to a few meters or feet deep. This level of detail is essential for identifying subtle variations in soil properties or natural geological structures that may not be apparent from surface observations alone.

Geophysics: your ally in ensuring a safe and secure home

Geophysical hazards like earthquakes, landslides, sinkholes, and subsurface voids pose significant risks to residential properties. By detecting these hazards’ size, location, and depth and conducting a comprehensive home safety assessment, you can identify potential vulnerabilities and take proactive steps to protect your home and family.

Geophysical methods such as seismic, GPR, and ERI survey imaging offer noninvasive, quick ways to evaluate the subsurface conditions underneath your home, assess its structural integrity, and evaluate its risk level. Addressing any issues identified through these surveys can enhance your home’s stability and resilience against natural geohazards.

Investing in geophysics-based mitigation strategies improves your home’s safety, reduces repair costs, and increases property value. As the demand for geophysics expertise in the housing industry grows, hiring experienced professionals can help you make informed decisions about your home’s safety and resilience.

Ready to take the next step in safeguarding your home? Let’s talk about how to avoid structural risks.

* Nothing in this article is to be construed as legal advice. All information in this article is general information for the public.