II. Destruction by quakes

II. Destruction by quakes

A. Ground shaking –most damage, by surface waves

1. Bedrock –the least amt. of damage ex. P.V. hills
2. Sediment –more amt. of damage ex: South Bay

P. 3. Water saturated sediment –worst damage,

greatest shaking…like jello ex. Harbor....landfill

B. Ground failure –most danger to us

P. 1. Liquification = water-saturated sed. flows during Q.
-bldgs. sink or tilt…as if on quicksand

P. 2. Landslides –destabilizes slopes in mts.
-especially if wet, too.
Figure 1

C. Tsunamis

P. - due to vertical motion of the seafloor........ subduction zn

- go 500 mph, arrive as series of surges every 20 min.= floods….......

P. - damage………………
ex: 2004 Indonesia = 280,000 dead

P. -also undersea landslides…...... ex. Hawaii......

1) Seiche = sloshing back + forth in lake or harbor
ex: L.A harbor? S.F. Bay?

D. Fire + Destruction during quake
- shaking breaks gas lines, water, sewer (regional, too…)

- closed stores, power off, no phones
* most important= don't run out during quake.....

E. Damage Prevention

- avoid low coastal area housing

- have emergency water, food, first aid kits, shoes (home + car!)

P. - Retrofitting = quake-proofing freeways, bridge, bldgs.

III. Earthquake Prediction – can’t predict when, just where…..

A. Seismic Risk Maps
P. -“probability” (based on past Q.s + active flts.)

and “intensity” (size of flt.s and ground….)
- ex. 3/4 of all US damage in Calif. …..1/3 in L.A. County!

A. PreCursors = before quake
- after much research ($),
- not reliable = don’t occur before most Q’s
1. Elevation change-use satellites (GPS)
2. Tilting – use tilt meters
3. Change in water and radon levels in wells
4. Animals = often can detect p + s waves

C. Quake Warning System = possible w/ SAF

- Problems: $, false alarms, panic, lawsuits…….

D. Seismic Gaps…useful…... where.........

P. =parts of flt. that haven’t moved recently = “overdue”
1. S.F. and Mexico City in ‘80s (6000 dead)

P. 2. “The Big One”= San Bernardino area of S.A.Flt........last in 1680

3. Oreg./Wash. = predicted 9.0, based on:

a. mud layers (every 500 yrs.) \

c. Native American oral……. /

4. 
   Indonesia and Japan …. recent, predictable locations
   

.

IV. Identifying Faults on surface
P. A. Epicenter Maps (fault maps)
.

B. Rocks along faults:
1. Fault Clay = Q.s grinds rock into clay (impermeable)
P. 2. Folded + offset rock layers
3. Slickensides……….

C. Land Features…seen when driving or flying

P. 1. Straight valleys …… ex. S. Andreas Flt. \
2. Springs…..water rises ex. Palm Springs } fault clay

3. Sag ponds (marsh) ex. Lake Elsinore /

P.

4. Straight fault “scarps” (super cliffs) ex. PV and Hollywood

P. 5. Offset streams, etc. ex. Orange Cnty...91 fwy

V. Distribution of Earthquakes

A. Plate boundaries = 95% of Q’s
P. 1. Conv…subd…Pacific Rim..... huge Q.s
2. Diverg…R.V…Mid ocean...... small Q.s
3. Transf…SAF... Calif. …......... big Q.s

B. Inside Plates (“intraplate” = inside plates)

P. ex. Missouri 1812 ……. ancient Rift V.

Geologic Time (ch. ) ….. history of earth

I. Relative Dating –1800’s…….

- compare rocks…..put rocks and fossils in order…old to young age
.

A. Geology Rules –1790’s = J. Hutton

P. 1. Law of superposition
-lower sediment rock beds =older
.

P. 2. Original horizontality

- sediment was horizontal when deposited
- any tilting or folding occurred later
.

P. 3. Cross cutting
- magma intrusion cut through older rock.
- faults cut through older rock.
.

B. Unconformities –interruptions in rock layers... missing history

P. =long time when these occurred:

1. Uplift….....tilting/folding….
2. Erosion.....................
3. Drop …. deposition again on top

P. 1. (Disconformity) - common
=beds stacked parallel..…uncomf.
.

P. 2. Angular Unconformity *
=horizontal layers over tilted layers
- due to uplift + tilt + erosion + drop (depos….)...m.y.s

P. 3. Non-Conformity
- layers over nonlayered rock like “granite”
ex: granite in Calif.

P. C. Solving geologic puzzles

D. Correlation = match rk layers ...same age...over big areas
1. Similar rock types – (rare) unique rk. (like fingerprint)