Active and Neotectonic Structures

1) What's the difference?2) Methods in active tectonics

3) Methods in neotectonics4) 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 measurement- what 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?

Good? Funding for geology?

Seismic hazard

Bad: destruction of propertyand life

What do we need to know, in order to predict

earthquakes??

(1) aseismic movements that occur in between earthquakes

The wave of the future-GPSGlobal Positioning System

Satellite navigation system

Accurate and precise knowledge of motionover 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 orogenesis- diffuse? 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 advancementsare simply awesome!

Wide-area, high-precisionsurveying from Space

Satellites beam microwaveradiation (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

Reverse fault

Strike-slip fault

San Gorgonio, CA

Paleoseismology

Paleoseismology:results for one faultsystem

Fault-scarp profiling- gives displacement and age—as well as other interesting info regarding structure

Laser theodolite for surveying. Gary Axenwishes that a satellite would fly over and beamdown those microwaves!

A cheaper way tofly!

400 m in 10000 yrs

40 mm per year

Long term plate motion- 5 cm/yr

Neotectonic mapping

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".