Earthquakes and Water
Offset Fence, Marin County
FAULTING About one kilometer northwest of Woodville this fence was
offset 2.6 m by the main fault. Note the swerve in the fence as it
approaches the fault-trace. The total displacement of the straight
San Andreas Fault
Any fault with a slip surface that does not reach the Earths surface.
Presence of faults can sometimes be determined from folding of
overlying rocks (or seismic imaging.)
Real problem in Southern CA.
You dont really know its
Rock Dating & Volcanoes
Relative Dating: Key Principles
o Law of Superposition: A bed of rocks is older than the rocks above it,
rocks on top are younger.
o Principle of Original Horizontality: Sedimentary layers are typically
For a water source to be permanent it needs to intersect the water table
The type of rock determines a lot about the groundwater flow
Porosity: % pore volume of solid:
Primary (formed when rock formed)
Secondary (formed by later - chemical
Morphology of Edge of Continent
Precipitous change in depth on continental slope marks change from
continental to oceanic crust
Tectonics controls a significant amount of coast morphology:
Continental shelf size.
Lack of extensive conti
Sedimentary & Metamorphic Rocks
Very Common Sedimentary Rocks
i. Sandstone sand usually from the beach or desert
ii. Mudstone/Shale Made of mud or very fine grained material. Usually
deposited in deep(er) water.
iii. Limestone Deposited shells of dead cri
Geologic Structures: Faults and Folds
o Strike: trend of a horizontal line alone the planar surface
o Dip: Angle of inclination from horizontal to the plane of the inclined
surface measured perpendicular to strike or direction water would
run down place
Volcanoes and Campus Fieldtrip
Requires melting point depression associated with the cycling of water
back into the Earth via subduction.
Subduction cycles water back into the mantle.
Water can cause melting point depression in the mantle wedge and i
The granitic rocks of the Sierra Nevada
Ancient plutons under a volcanic arc Plutons grow incrementally with
A giant plutonic intrusion is called a batholithic.
Classification of plutonic rocks
Based upon the percentage of three miner
Fossil organisms succeed each other in systematic fashion
Used as guides to the age of the rocks in which they are preserved
Organisms that existed during limited periods of geologic time and over a wide area
Usually commonly preserv
CA Sedimentary Rocks
Sandstone mostly deposited in marine environmentsimportant for groundwater and hydrocarbon
Shale/mudstone hydrocarbon sourcs, diatomaceous earth- significant but volumetrically less important
Chertcoast ranges and western Si
Igneous & Sedimentary Rocks
Compositions are determined by chemistry of the source rock, the
pressure and temperature and volatile content (water and carbon dioxide)
of the source region.
Ring of Fire associated with subduction zones.
Metamorphic Rock Key
1. Green Schist
7. Blue Schist
Section 3: Metamorphic Rocks
Rocks that are foliated:
o Green Schist
o Blue Schist
Q2. Metamorphic Grade
Section 1: Properties of Common Minerals
Quartz: Two crystals one pink and one clear
Chert: Cleavage/ size difference
Feldspar: Different colors
Talc: Slight variations in color
Garnet: Color and crystal structure
Gold and Geologic Structures
What is the geology of Gold Country?
The contact between old seafloor and granite.
Western Sierra Metamorphic belt composed of basalts, peridotite or
serpentine (ultramafic rocks), and associated sediments. Remnants
The hydrologic cycle, water in motion.
In the Big Picture, the water cycle includes the entire earth!
Subduction brings water back down into the Earth, the water causes
volcanoes to form, volcanoes spew water back into
Glaciers & Climate
The periodic advance and retreat of large ice sheets and glaciers on
We currently live in the interglacial when the continental ice sheets
are in retreat
Interglacial: The periodic advance and retreat of la
Predominate Ice Age Causes
Shape of orbit, more elliptical (should be weakest effect but it
seems to be dominate)
Changes in tilt of rotation axis
Wobbling of axis
Ellipticity cycle is about 100,000 years
Axial tilt c
Formation of Sand Dune
Most common type of dune in which crest forms perpendicular to wind
direction and slip face is inclined down- wind.
Amount of sand wind direction, duration, and strength can influence dune
Colors of the Desert: Red
Deserts can be found at:
Low Latitudes (between the Tropic of Cancer ~30N and the Tropic
of Capricorn ~30S)
High Latitudes (above the Arctic and below the Antarctic circles)
These deserts are generally a result of the Earths atmospheric
What drives plate tectonics?
Convection caused by physical movement in the core. Plates sit on
convection cells and move accordingly.
Heat causes upwelling which in turn creates hot spots & volcanoes
Cold causes down-welli
Fault location and displacement can be determined by many surface
The San Andreas fault is a right-lateral transform (or strike-slip)
Bends in strike-slip faults like the San Andreas produce areas on
Earthquakes Part II
Seismic waves travel curved paths through the Earth because
properties change continuously with depth.
Different materials have different seismic velocities.
Seismic waves move the earth the same way light waves move
Introduction to Tectonic Plates
Plate tectonics is the accumulation of what we see
geographically see today.
There are 14 major plates
The crust and mantle are mostly rocks (Mg, Fe, Si)
Core is mostly iron.
Types of Crust
Granite is Felsic
Plutonic (Intrusive (cool in the earth)- Granite
Volcanic (extrusive (cools outside the earth)- Rhyolite
Basalt is mafic, most common rock on earth
Andesite is in the middle