Active and Neotectonic Structures
1) What's the difference?
2) Methods in active tectonics
3) Methods in neotectonics
4) Implications for structural geology
5) Consequences for Society
Time scales
• Tectonics- study of large scale deformations
and Earth evolution processes at scales of
millions to tens of millions of years; focus of this
class
• Neotectonics = thousand to tens of thousand
years
• Active tectonics = happens during a person's
lifetime
Uniformitarianism
Present is key to the past
Or is it?
Methods in Active tectonics
1) Seismology
2) Measuring recent movements
– Surveying
– GPS techniques
– Radar interferometry
Earthquakes occur
all the time- all over
the world
They produce
ground motion
(seismic waves), that
we can measure
>3000 seismological
observatories around the
world, continuously
recording seismic waves
How long did it
take seismic
waves to travel
from Alaska to
Tucson?
Real-time action; Real-time measurementwhat can we learn from seismology about
structural geology??
1) Location and depth of faulting (brittle-ductile
transition)
2) fault plane solutions- orientation of fault and sense of
slip- geometry and kinematics
3) Energy release- size of fault, rupture
characteristics- unidirectional, bidirectional, chaotic?
Seismic hazard
Bad: destruction of property
and life
Good? Funding for geology?
What do we need to know, in order to predict
earthquakes??
(1) aseismic movements that occur in
between earthquakes
The wave of the future-GPS
Global Positioning System
Satellite navigation system
Accurate and precise knowledge of motion
over timescales of years
What we are learning from GPS
1) Plate tectonic assumptions OK- but only to first
order- Within plate deformation can be huge
2) How continents deform during orogenesisdiffuse? plate like?
3) What parts of faults are slipping vs. what parts
are "locked" up- important for EQ predictions
4) unprecedented knowledge of recent movements
on Earth
GPS is great, but requires lots of stations and time to
wait around.
Scientists are greedy- we want more data on ground
motion and with less effort- is it possible?
Scientific advancements
are simply awesome!
Wide-area, high-precision
surveying from Space
Satellites beam microwave
radiation (radar) down on
Earth
The Earth reflects back to the satellite microwaves
of different phases that yield X,Y,Z information.
Two passes of a satellite with imaging radar over
the same area produce two images. The
difference between two images provides the
displacement field over the entire area (often, 100
km 100 km) between the time of the two passes.
A simple, schematic example
A real example- ground motion due to an
earthquake in a thrust belt
Movement of glaciers over six days- think about
how many GPS stations would be required to
provide this kind of detailed information
Displacement due to an EQ in Turkey. Can also
determine displacement in between EQ's!
Landers Earthquake
This technique is called InSAR- for Interferometric
Synthetic Aperture Radar. The potential is endless!
It is estimated that a magnitude 8 or larger
earthquake in a major metropolitan area,
such as Los Angeles or Tokyo would cause
more than 40,000 fatalities, up to 250,000
injuries, and $100 billion dollars in damage
What else do we need to know to be able to
predicts earthquakes?
Study the earthquake cycle- recurrence intervals
of major events through neotectonic studies
1) study deformed historic sites of known ages
(Great Wall of China)
2) Paleoseismology
3) offset geomorphologic surfaces + surface
dating
Normal fault
Strike-slip fault
Reverse fault
Paleoseismology
San Gorgonio, CA
Paleoseismology:
results for one fault
system
Fault-scarp profiling- gives displacement and age—
as well as other interesting info regarding structure
Laser theodolite for
surveying. Gary Axen
wishes that a satellite
would fly over and beam
down those microwaves!
A cheaper way to
fly!
Neotectonic mapping
400 m in 10000 yrs
40 mm per year
Long term
plate motion- 5
cm/yr
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.
Assignment
Visit the following website:
http://quake.wr.usgs.gov/research/index.html
http://quake.wr.usgs.gov/research/deformation/
modeling/index.html
Surf around. Check out the cool animations!
Download 4 of your favorite geology-related
images. Then email to me
(pkapp@geo.arizona.edu). This will be graded
as a "What is it quiz".