International Building Code 2018 (IBC 2018)

Heads up: There are no amended sections in this chapter.
The intent of these provisions is to provide the minimum level of effort required when investigating the potential for surface fault rupture and fissuring in Clark County, Nevada. Additional effort beyond these provisions may be required at certain sites due to their complexity and the nature of the proposed improvements.

The following words and terms shall, for the purposes of this appendix, have the meanings shown herein. Refer to Chapter 2 of this code for general definitions.

Differential Land Subsidence. Subsidence across pre-existing faults.

Earth Fissure. Ground cracks or voids found in the near surface of the earth. Earth fissures are believed to have formed in response to tensional or horizontal stresses from regional land subsidence or to ground shaking from earthquakes resulting in ground deformation or both.

Fault. A fracture or a zone of fracturing along which there has been displacement of the sides relative to one another parallel to the fracture. Faults will be classified as follows:

  1. Fault, Holocene Active: A fault that has moved within the last 11,000 years.
  2. Fault, Late Quaternary Active: A fault that has moved within the last 130,000 years.
  3. Fault, Quaternary Active: A fault that has moved within the last 1,600,000 years.
  4. Fault, Inactive: A fault without recognized activity within the past 1,600,000 years.

Fault Line (Trace). The line or trace of a fault plane on the ground surface or on a reference plane formed by the intersection of a fault and the earth's surface.

Fault Scarp. A steep slope or cliff formed directly by movement along the fault and representing the exposed surface of a fault before modification by erosion and weathering.

Fault Zone. A fault expressed as a zone of numerous small fractures or angular rock fragments or fault gouge (finely ground rocks). A fault zone may be up to hundreds of feet wide.

Geotechnical Investigation. Report prepared per sections 1803.2 through 1803.6.

Land Subsidence. The gradual downward settling or sinking of the earth's surface.

Lineament. Linear or curvilinear geomorphic feature interpreted to be of tectonic origin which does not clearly exhibit fault scarp characteristics and cannot be differentiated by age.

Subsidence-Induced Movement. Renewed movement of a fault induced by historical land subsidence. Subsidence induced movement may occur on a fault regardless of earthquake activity on the fault.

Surface Rupture. A fracture or break in the ground surface resulting from faulting, fissuring, or land subsidence.

All Geotechnical Investigation reports shall address the requirements of IBC section 1803.5.11 regardless of the specific requirements of this appendix.

An evaluation of sites for potential surface rupture or hazards due to differential subsidence and fissuring as described in this appendix shall be performed when any of the following conditions apply:

  1. A fault has been previously mapped or otherwise documented to exist within 1,000 feet from the site.
  2. When a fault has been previously mapped within the limits of the property.
  3. When required by the building official.

The registered design professional performing the evaluation must determine what is appropriate and necessary.

Exception: At the option of the building official, the following structures may be exempt from the investigation described in this appendix:
  1. Dwellings and accessory structures (e.g. casita, patio covers, decks, canopies, etc.) associated with a single lot, single family residence. In this case, the fault location may be historically approximated by the registered design professional through historical research and shall be shown in the Geotechnical Investigation report. A setback of at least fifty (50) feet from each side of the historically approximated fault edge shall be established.

A registered design professional shall perform an evaluation. The evaluation shall include:

  1. Research of available information, such as geologic maps, technical publications, historical imagery, etc.
  2. A surface evaluation.
  3. A subsurface investigation as described in Section P104.1.3 if any Quaternary-age or more recent surface rupture is mapped or otherwise documented to exist within the limits of the property or within 50 feet from the property line as noted in section P104.1.2.2.

The methodology and results of the evaluation must be properly documented in the Geotechnical Investigation report (See section P105 for reporting requirements). Some of the evaluation methods described below should be carried out beyond the site being investigated.

Review of the region's seismic history, based on existing maps and technical literature.
  1. Historic earthquakes, epicenter locations, and magnitudes in the vicinity of the site.
  2. Location of fault traces that may affect the site, including maps of faults and a discussion of the tectonics and other relationships of significance to the proposed construction.
  3. Location and chronology of other earthquake-induced features, such as settlement, landslides and liquefaction.
  4. Review of local groundwater data (water-level fluctuations, groundwater impediments, water quality variations, or anomalies indicating possible faults).
  1. Identify and locate any faults, scarps, and fissures in the vicinity of the site.
  2. Review available land level lines of past ground surface movement in the vicinity of the site, including degree of differential subsidence across nearby faults and proximity of regional subsidence bowls.
  3. Review groundwater development in the vicinity including the location of nearby high-capacity wells. Review available well maintenance records of nearby wells for signs of possible subsidence-induced damage.
  4. Review of subsurface units from available well driller's logs for nearby water wells and available historic water level data from nearby wells (e.g. the State of Nevada Department of Water Resources through their website provides free access to Nevada hydrology data, including well logs and historic and current water levels).
Analysis shall include interpretation of aerial photographs and other remotely sensed images for fault-related topography, vegetation, soil contrasts, and lineaments of possible fault or fissure origin. Where possible, analysis may include low-sun-angle aerial photography and/or aerial reconnaissance.
A registered design professional shall inspect the site for indicators that a fault exists or may exist onsite. The inspection may extend beyond the limits of the site being evaluated.
  1. Conduct visual inspections for signs of ground movement (distress) of man-made structures on adjacent developments. Review available geotechnical reports to determine the geotechnical conditions of sites in the area.
  2. Mapping of surface features, including geologic units and structures and topographic features both on and beyond the site.
  1. If any Quaternary-age or more recent surface rupture is mapped or otherwise documented to exist within the limits of the property or within 50 feet from the property line, the feature(s) shall be further investigated as described in section P104.1.3.

    Note: In the event that the subsurface investigation cannot be performed beyond the limits of the property, the registered design professional shall perform the subsurface investigation within the limits of the property, as close as practical to the feature of interest, to disprove the possibility of the fault being present onsite.

The subsurface investigation, if required per section P104.1.2.2, shall consist of trenching and other excavating, with appropriate logging and documentation to permit detailed and direct observation of exposed geologic units and features. In cases where the geologic feature of interest is below the practical limit of the excavation (e.g. fault rupture has been obscured by deep alluvium, etc.), the registered design professional may consider the use of other techniques, such as geophysical surveys, to obtain adequate subsurface information. The following methodologies may be used in a subsurface investigation:
  1. This includes trenching across potentially active fault zones to determine the following: location and recency of movement, width of disturbance, physical condition of fault zone materials, type of displacement, geometry of fault features, slip rate, and recurrence interval.
  2. Borings or test pits to collect data to evaluate depth and type of materials present, groundwater depth, and to verify fault-plane geometry. Data points should be sufficient in number and adequately spaced to permit correlations and interpretations.
  3. Geophysical surveys conducted to facilitate the evaluation of the types of site materials and their physical properties, ground water conditions, and fault displacements. When geophysics is utilized for fault mapping, a minimum of two arrays perpendicular to the suspected fault trace shall be performed. The geophysical exploration program, including the number of geophones, type of geophones, spacing and other survey parameters, shall be selected by the registered design professional.
Detailed trench logging at the site should focus on determining the location and possible causes of fissuring. Compare trenches across fissures in areas on the site and in areas where fissures are not observed at the surface. Width of the fissure zones and the general geometry and depth of fissures shall be determined.
The following subjects shall be addressed in any investigation of sites for potential surface rupture or hazards due to differential subsidence and fissuring. The results of the investigation shall be presented as an appendix to the Geotechnical Investigation report.
Geotechnical Investigation reports shall include the following information.
  1. Purpose and scope of investigation.
  2. Geologic setting.
  3. Site description and conditions, including information on geologic units, aquifer conditions, graded and filled areas, vegetation, existing structures, and other factors that may affect the choice of investigative methods and the interpretation of data.
  4. Methods of investigation utilized.
  5. Conclusions.
    1. Location (or absence) of all surface ruptures on or adjacent to the site.
    2. Type of faults and nature of anticipated offset: Direction of relative displacement, and maximum possible displacement.
    3. Statement of relative risk addressing the probability or relative potential for future surface displacement. This may be stated in semi-quantitative terms such as low, moderate, or high, or in terms of slip rates determined for specific fault segments.
    4. Degree of confidence in, and limitations of, the data and conclusions.
  6. Recommendations
    1. The minimum Setbacks shall be per section 1808.10. If the recency of movement cannot be determined, then the fault shall be assumed to be Holocene for minimum setback purposes.
    2. The faults and minimum setback shall be clearly shown to scale on the grading plan, plot plan and final map; no portion of the foundation system shall be constructed within that zone.
    3. Need for additional studies, or inspection during construction.
The Geotechnical Investigation shall list all references used in the investigation.
  1. Literature and records cited or reviewed; citations should be complete.
  2. Aerial photographs or images interpreted including type, date, scale, source, and index numbers.
  3. Other sources of information, including well records, personal communications, and other data sources.
Illustrations are essential to the understanding of the report and to reduce the length of text. Most of these items would typically be applicable.
  1. Location map - identify site locality, significant faults, geographic features, regional geology, seismic epicenters, and other pertinent data. A 1:24,000 scale is recommended.
  2. Site development map. Show site boundaries, existing and proposed structures, graded areas, streets, exploratory trenches, borings, geophysical traverses, and other data. Recommended scale is 1 inch equals 200 feet (1:2,400) or larger.
  3. Geologic map. Shows distribution of geologic units (if more than one), faults and other structures, geomorphic features, aerial photo lineaments, and springs, on topographic map at 1:24,000 scale or larger. Can be combined with items 1 or 2.
  4. Geologic cross-sections.
  5. Logs of exploratory trenches and borings. Show details of observed features and conditions; should not be generalized or diagrammatic. Trench logs should show topography and geologic structure at the same horizontal and vertical scale.
  6. Geophysical data and geologic interpretations.
  7. Photographs of scarps, surface ruptures, trenches, samples, or other features that enhance understanding of the site conditions.
Supporting data not included above (e.g. water well data).
Signature of the registered design professional who conducted the evaluation.
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