1. ESP 179- Winter 2012
Geology and Soils
January 24, 2012
Instructor: Trevor Macenski

2. Outline
 Review CEQA Checklist Questions
 Seismic Hazards in CA
 Alquist-Priolo Earthquake Fault Zoning Act
 Seismic Hazards Mapping Act
 Common Geologic Hazards
 Impact Analysis Approach
 Sample Discussion and Analysis

3. Geology and Soils
 Appendix G Checklist: Geology and Soils
 Expose people or structures to substantial adverse effects
 Alquist-Priolo Fault Zone
 Seismic ground Shaking
 Ground failure/Liquefaction
 Landslides
 Loss of top soil
 Lateral Spreading
 Expansive Soils
 Soils and Septic System

4. Appendix G: Checklist Questions
Projects that have large

5. Appendix G: Checklist Questions

6. Seismic Hazards
 Pose a substantial danger to property and
human safety.
 Seismic hazards present in California
include:
 Ground rupture along faults
 Strong seismic shaking
 Liquefaction, Lateral Spreading, Lurching
 Landsliding
 Slope failure
 Hazardous Minerals
 Tunamis

7. Fault Rupture
 Fault rupture is a seismic hazard that
affects structures sited above an
active fault.
 The hazard from fault rupture is the
movement of the ground surface
along a fault during an earthquake.
 Creep= Slower moving fault action
 Earthquakes-
 Strike-slip
 Normal
 Thrust
Infrastructure often can’t handle Creep or Earthquakes

8. Ground Shaking
 Ground shaking depends on several
variables:
 Earthquake magnitude
 Epicenter distance
 Local geology and Soils Thickness
 Seismic wave-propagation properties of
unconsolidated
 Materials
 Groundwater conditions
 Topographic setting
Sample Modeling

9. Richter vs. MMI
 Richter Scale
 Measurement comparison between earthquakes
 Evaluates magnitude used for scientific comparison
 Only accounts for the actual slip that is generated
 Actual damage= Propagation of seismic or ground
waves as a result of initial failure
 Loose materials tend to amplify ground waves,
while hard rock can quickly attenuate them,
causing little damage to overlying structures.

10. Richter vs. MMI
 Modified Mercalli Intensity (MMI)
 Scale provides a useful qualitative assessment
of ground shaking.
 The MMI Scale is a 12-point scale of
earthquake intensity:
 Local effects experienced by people
 Structures
 Earth materials.
 Each succeeding step on the scale
describes a progressively greater amount
of damage at a given point of observation.

11. Alquist-Priolo Earthquake
Fault Zoning Act
 Passed in 1972
 Intent: to mitigate the hazard of surface
faulting to structures for human occupancy
 Purpose: Direct result of the 1971 San
Fernando Earthquake
 Extensive surface fault ruptures that damaged
numerous homes, commercial buildings, and
other structures.

12. Alquist-Priolo Cont.
 Requires the State Geologist to establish
regulatory zones (known as Earthquake Fault
Zones) around the surface traces of active faults
and to issue appropriate maps.
 The maps are distributed to all
affected cities, counties, and state agencies for
their use in planning and controlling new or
renewed construction.
 If an active fault is found, a structure for
human occupancy cannot be placed over the
trace of the fault and must be set back from
the fault (generally 50 feet).
 Project will require site specific geotech mitigation

13. Seismic Hazards Mapping Act
 Passed in 1990
 Intent: Directs the Department of
Conservation, California Geological Survey
to identify and map areas prone to
liquefaction, earthquake-induced
landslides and amplified ground shaking.
 Purpose: The SHMA was passed by the
legislature following the 1989 Loma Prieta
earthquake.

14. SHMA Cont.
 Geologists in the Seismic Hazard Zonation
Program gather existing geological, geophysical
and geotechnical:
 Produce the Seismic Hazard Zone Maps.
 Designate as Zones of Required Investigation (ZORI)
 Prone to liquefaction and earthquake–induced landslides.
 The SHMA requires site-specific geotechnical
investigations within ZORI’s
 To identify and evaluate seismic hazards and formulate
mitigation measures prior to permitting

15. Ground Failure
 Ground failure includes:
 Liquefaction
 Liquefaction-induced phenomena:
Lateral spreading
Lurching

16. Liquefaction
 Liquefaction is a process by which sediments below the
water table temporarily lose strength during an earthquake
and behave as a viscous liquid rather than a solid.
 Liquefaction is restricted to certain geologic and hydrologic
environments, primarily recently deposited sand and silt
in areas with high groundwater levels.
 The process of liquefaction involves seismic waves passing
through saturated granular layers, distorting the granular
structure and causing the particles to collapse. This causes
the granular layer to behave temporarily as a viscous liquid
rather than a solid, resulting in liquefaction.
 USGS has maps to identify areas: MAP

17. Lateral Spreading and Lurching
 Lateral spreading
 is lateral ground movement, with
some vertical component, as a result
of liquefaction.
 The soil rides on top of the liquefied
layer
 Lurching
 is the movement of the ground
surface toward an open face when the
soil liquefies. An open face could be a
graded slope, stream bank, canal face,
gully, or other similar feature.

18. Landslide Hazard Mapping Act
 Produced from 1986 through 1995, as
directed by the now-repealed Landslide
Hazard Mapping Act.
 Online Resource: MAPs

19. Landslides
 Categorized as either 1) rock, 2) soil, or 3)
rock and soil.
 Rock= refers to hard or firm bedrock that
was intact and in place prior to slope
movement.
 Soil=means unconsolidated particles or
poorly cemented rock or aggregates.
 Soil is also distinguished further on the basis of
texture:
Debris (coarse fragments)
Earth (fine fragments)

20. Landslide Classification
 1) Falls: Masses of soil or rock that dislodge from steep
slopes and free-fall, bounce, or roll downslope.
 2) Topples: Move by the forward pivoting of a mass
around an axis below the displaced mass.
 3) Spreads: Commonly induced by liquefaction of material
in an earthquake, move by horizontal extension and shear
or tensile fractures.
 4) Slides: Displace masses of material along one or more
discrete planes.
 Rotational: Sliding the slide plane is curved and the mass
rotates backwards around an axis parallel to the slope
 Translational: Sliding the failure surface is more or less planar
and the mass moves parallel to the ground surface
 5) Flows : mobilize as a deforming, viscous mass without
a discrete failure plane.

21. Hazardous Minerals of CA
 Asbestos-Inhalation of asbestos fibers may
cause cancer.
 Most commonly, asbestos occurrences are associated
with serpentinite and partially serpentinized ultramafic
rocks.
 Mercury- Mercury from historic mercury mines
or gold mines has entered a number of
watersheds in California.
 Radon- Gas is a naturally-occurring, radioactive
gas that is invisible and odorless. It forms from
the radioactive decay of small amounts of
uranium and thorium naturally present in rocks
and soils.

22. Sample EIR Discussion

23. Significant Geology and Soil
Impacts?
 What are a few types of projects?
 Residential project close to a fault
 Natural Gas Pipeline close to fault
 Oceanfront Development
 Other?

24. Questions?
Thank You