Earthquake Notes

Crustal Deformation

REVIEW:

So far we have found that convection currents cause several

things to happen. 1. Continental movements

2. Earthquakes 3. Volcanoes4. Mountains

ISOSTATIC ADJUSTMENT up and down movements of crust.

This adjusts for uplift and weathering of mountains.

These movements cause…

STRESS ON THE ROCKS!!!!

Stress - the amount of force Stress - the amount of force placed on the rocks, also called placed on the rocks, also called STRAIN.STRAIN.

• There are 3 TYPES OF STRESSThere are 3 TYPES OF STRESS

–COMPRESSION Pushing Pushing together of rockstogether of rocks

–TENSION Pulling apart of rocksPulling apart of rocks

–SHEARING Lateral (side to Lateral (side to side) tearing of rocksside) tearing of rocks

–With Continental Movements comes With Continental Movements comes breaks and folds in the rocks of the breaks and folds in the rocks of the continents.continents.

3 TYPES OF FOLDS

• Limbs - sides of the fold or rock - sides of the fold or rock layers before and following a fold.layers before and following a fold.

1. ANTICLINE - an upward fold in - an upward fold in rock layers where oldest rock layer rock layers where oldest rock layer is in the center of the fold. Limbs is in the center of the fold. Limbs fold down, it forms a ridge (hill)fold down, it forms a ridge (hill)

3 TYPES OF FOLDS22. . SYNCLINE_ a syncline is a downward _ a syncline is a downward

fold in the rock layers where youngest fold in the rock layers where youngest rocks are in the center. Limbs fold up, rocks are in the center. Limbs fold up, it forms a valley.it forms a valley.

3 TYPES OF FOLDS3. MONOCLINE_ slight fold in one area but _ slight fold in one area but

both limbs remain horizontal both limbs remain horizontal

4. Dip (steepness) of the limbs reflects the 4. Dip (steepness) of the limbs reflects the intensity of the fold. intensity of the fold.

5. Strike is the compass direction of the fold 5. Strike is the compass direction of the fold of the rock layer. of the rock layer.

6. Folding can be so severe the rock layers 6. Folding can be so severe the rock layers are overturned or upside down. are overturned or upside down.

2 TYPES OF BREAKS IN ROCK LAYERS:

• FRACTURE__ Break in rock layers Break in rock layers where no movement has occurred.where no movement has occurred.

• FAULT_ Break in rock layers where _ Break in rock layers where movement has occurred or is movement has occurred or is currently happening. There are currently happening. There are several in several in Kentucky

• Movements along faults account for Movements along faults account for 80% of all earthquakes, the other 80% of all earthquakes, the other 20% from plate boundaries.20% from plate boundaries.

2 SIDES TO EVERY FAULT:2 SIDES TO EVERY FAULT:• Look at it this way, imagine you are Look at it this way, imagine you are

standing on a fault:standing on a fault:

• HANGING WALL- surface of rock HANGING WALL- surface of rock directly above the fault plane. (over directly above the fault plane. (over your head)your head)

• FOOTWALL- surface of rock directly FOOTWALL- surface of rock directly below the fault plane. (your are feet on below the fault plane. (your are feet on it)it)

UNC geologists illustrating the concept of footwall and hanging wall at a small fault near Las Vegas, Nevada. Their feet are on the footwall, and the hanging wall is hanging over their heads. This is a small normal fault. Grooves and scratches on the fault plane run down the dip of the plane.

MAJOR TYPES OF FAULTSMAJOR TYPES OF FAULTS•NORMAL FAULT- occurs when hanging - occurs when hanging

wall moves down. You think it is wall moves down. You think it is NORMAL because gravity would act NORMAL because gravity would act on it so it drops down on it so it drops down

• This is caused by a This is caused by a Tension force on force on this type of fault.this type of fault.

• Convections cells pulling on rocks of Convections cells pulling on rocks of crust cause tension force.crust cause tension force.

MAJOR TYPES OF FAULTSMAJOR TYPES OF FAULTS

•REVERSE FAULT- hanging wall moves - hanging wall moves up due to compression forces, this up due to compression forces, this moves opposite of the normal fault. moves opposite of the normal fault.

• Convections cells pushing on rocks of Convections cells pushing on rocks of crust cause the compression force.crust cause the compression force.

MAJOR TYPES OF FAULTSMAJOR TYPES OF FAULTS

• THRUST FAULT- Special kind of - Special kind of reverse fault, the angle of the fault reverse fault, the angle of the fault plane is very low, almost horizontal.plane is very low, almost horizontal.

• STRIKE-SLIP FAULTSTRIKE-SLIP FAULT -( Transform -( Transform fault) The rocks move horizontally fault) The rocks move horizontally in relation to each other by in relation to each other by

• Most common at transform Most common at transform boundaries like: San Andreas Fault boundaries like: San Andreas Fault in California.in California.

MOUNTAINS FORM IN 3 MOUNTAINS FORM IN 3 WAYSWAYS

• CONTINENTAL VS OCEANIC PLATES_ CONTINENTAL VS OCEANIC PLATES_ Produces much crustal deformation. Produces much crustal deformation. High mountains produced, mostly High mountains produced, mostly volcanic because the ocean plate is volcanic because the ocean plate is subducted beneath the continent. subducted beneath the continent.

– Ex Cascade Range.Ex Cascade Range.

MOUNTAINS FORM IN 3 MOUNTAINS FORM IN 3 WAYSWAYS

• OCEANIC VS OCEANIC_ Produces OCEANIC VS OCEANIC_ Produces little crustal deformation. Large little crustal deformation. Large volcanic mountain islands form. volcanic mountain islands form. Peaks of these volcanic mountains Peaks of these volcanic mountains reach from ocean floor to surface.reach from ocean floor to surface.

– Ex. Mariana Islands in North Pacific Ex. Mariana Islands in North Pacific form. form.

MOUNTAINS FORM IN 3 MOUNTAINS FORM IN 3 WAYSWAYS

• CONTINENTAL VS CONTINENTAL_ CONTINENTAL VS CONTINENTAL_ Produces intense crustal Produces intense crustal deformation with immense deformation with immense mountain ranges of folded and mountain ranges of folded and faulted mountains. faulted mountains.

– Ex Himalayas.Ex Himalayas.

4 KINDS OF MOUNTAINS4 KINDS OF MOUNTAINS

• FOLDED_ Highest mountains in the world, FOLDED_ Highest mountains in the world, rocks squeezed together like an accordion.rocks squeezed together like an accordion.

– Ex. Appalachian Ex. Appalachian

• PLATEAU_ Large areas of flat-topped rocks PLATEAU_ Large areas of flat-topped rocks high above sea level. Formed by thick high above sea level. Formed by thick horizontal layers of rock slowly uplifted. horizontal layers of rock slowly uplifted. Most are next to mountain ranges. Most are next to mountain ranges.

– Ex. Tibetan PlateauEx. Tibetan Plateau

4 KINDS OF MOUNTAINS4 KINDS OF MOUNTAINS• FAULT-BLOCK MOUNTAINS_ Sections FAULT-BLOCK MOUNTAINS_ Sections

of crust broken into large blocks and of crust broken into large blocks and shifted, up, down, or over other shifted, up, down, or over other sections. sections.

– Ex Nevada, Arizona, Utah…Ex Nevada, Arizona, Utah…

• GRABENS_ These develop when GRABENS_ These develop when steep faults break crust into blocks, steep faults break crust into blocks, then block(s) slips downward along then block(s) slips downward along normal faults. normal faults.

– Ex Death Valley Ca. Ex Death Valley Ca.

4 KINDS OF MOUNTAINS4 KINDS OF MOUNTAINS• VOLCANIC_ Molten rock erupts onto VOLCANIC_ Molten rock erupts onto

surface, on land, ocean floor. Some of surface, on land, ocean floor. Some of largest are along mid-ocean ridges. largest are along mid-ocean ridges. Others over hot spots. Others over hot spots.

– Ex Azores and Hawaiian islands.Ex Azores and Hawaiian islands.

• DOME_ Unusual, molten rock rises DOME_ Unusual, molten rock rises through crust, pushes up rock layers, through crust, pushes up rock layers, never melts through to surface. never melts through to surface. Eventually, cools and hardens, erosion Eventually, cools and hardens, erosion removes rocks over it leaving separate removes rocks over it leaving separate high peaks. high peaks.

– Ex Black Hills of South Dakota, Adirondack Ex Black Hills of South Dakota, Adirondack Mountains of New York State. Mountains of New York State.

Strike-slip fault

• The rocky blocks on either side of strike-slip faults, scrape along side-by-side, no vertical movement means no hanging or foot wall.

• The fault line ascends slowly from the lower right edge of the picture to beyond the center where some folding of the layers at the fault contact can be seen.

Thrust fault along Interstate-70, Silverthorne --- Younger rocks on the very bottom of this picture have been thrust under older rocks and pushed west (left) for several miles.

Reverse Fault

• Along a reverse fault one rocky block, the hanging wall, is pushed up relative to rock on the other side.

Normal Fault

• A normal fault drops rock on one side of the fault down relative to the other side. Take a look at the side that shows the fault and arrows indicating movement

• Fracture• Note the

number of fractures these are small others can be huge.

• Huge faults visible in the side of this canyon. This faulting occurred over 20,000,000 years.

This is what faulting can do to the surface of the earth during an earthquake. This faulting occurred during 1 earthquake.

Known Major KY Faults

FIGURE 16.--. Solid lines indicate fault traces.

Tension VS undeformed rock strata

Back to Normal

Shearing VS undeformed rock strata

Compression verses undeformed rock strata

This Anticline is 500 feet thick.

This Syncline is 4000 ft tall

This Monocline is barely 5 feet thick.