Transcript Document

Lecture 1/22/02 GEOS 304
Active and recent structures
Handouts and Powerpoint file
Objectives
• Neotectonics vs. active tectonics
• Earthquakes and faults
• Methods used to measure amounts and rates
of present day deformations
• Geologic clues for young deformation
• Deconstructing Hollywood and LA
Uniformitarianism
Present is key to the past
Or is it?
Time scales
• Tectonics- analyses large scale
deformations and Earth evolution
processes at scales of millions to tens of
millions of years
• Neotectonics- time scale= thousand to
tens of thousand years
• Active tectonics = years to tens of years
• 10,000,000- 100,000,000 = Orogenic scale
Our main scale of interest in this class
• 1,000-10,000 = Neotectonics
• 1-10 = Active tectonics
How do they compare?
Methods
• ACTIVE deformation: study of earthquakes,
monitoring with strainmeters and tiltmeters,
other geodetival techniques. NEW techniques:
continuous GPS and Radar interferometry
• NEO-deformation, study of deformed historic
sites of known ages , geochronology, + a variety
of other techniques
Active structures
Damages caused by earthquakes
Near field:
Ground cracks
Collapes of buildings
Death
What are earthquakes?
Obviously they are ruptures though the
Earth’s crust. I.e. they are faults
Normal fault
Strike-slip fault
Reverse fault
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Reverse fault
Normal fault
Strike slip
Normal fault
Strike-slip fault
Reverse fault
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
= funding for geology
Indonesia (unknown loc)
San Gorgonio, CA
Izmit earthquake 1999
The bed of this major river at the northern end of the
Chelungpu fault has been disarticulated by the fault.
The scarp hidden by the waterfall is about 7 meters high.
The bridge failed where it crosses the fault to the right a few
hundred meters, out of the frame of the photo. It is being
reconstructed in the same location.
Long term plate motion- 5 cm/yr
400 m in 10000 yrs
40 mm per year
En echelon fault
(compare to
Fig 6.148 in text)
Folds
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
The wave of the future-GPS
Lessons from GPS and geodesy
• Nothing is stable
• Plate tectonics assumptions are ok as first
order aprox. Within plate deformation can
be huge!
• Long term rates are comparable to short
term - but keep in mind the sudden release
of energy along earthquakes.
An example: faults in Los Angeles
View northward from the star-studded intersection of Hollywood and Vine.
The ramplike rise in the street just beyond the Capitol Records building is the scarp
of the Hollywood fault. Beyond the scarp and the freeway bridge are the Hollywood Hills,
raised by innumerable ruptures of the fault.
The Hollywood fault and anticline
Anticline
Fault tip
Fault
Summary
• Active and recent structures- provide the
foundation of interpretative structural
analysis;
• Faults: reverse, normal and strike-slip
• Folds: anticlines and synclines
• Lithospheric plates are not entirely rigid
• Structures form steady-state as well as
catastrophically (in large increments separated
by no deformation)
Please read the handout provided
today- Chapter 2 in Dennis
• It will give you additional information on
active and recent structures, pre GPS.
• Focuses on vertical deformation, and does a
good job of distinguishing between climate
vs. tectonic vertical motions.
Preview of Cottonwood