Kennebec River, Georgetown, ME

1
(No Transcript)
2
Kennebec River, Georgetown, ME Vanessa Lyons
3
Sea Caves, La Jolla, CA Samantha Bassman
4
Montmorency Falls, QC Emily Stuart
5
SEISMIC WAVES
6
SEISMIC WAVES
BODY WAVES
BODY WAVES transmit energy through the Earths
interior in all directions from the
earthquakes focus.
7
SEISMIC WAVES
BODY WAVES
PRIMARY or P-WAVES
Are the fastest seismic waves (6-7 km/sec). First
to arrive at earthquake station and be recorded
on a seismograph. Energy is a compressional wave
that alternates between compression and
dilation. Vibration is parallel to direction of
travel. Produces sharp jolts.
8
SEISMIC WAVES
BODY WAVES
SECONDARY or S-WAVES
Slower than P-waves (3.5 km/sec). Second wave to
arrive at earthquake station and be recorded on
a seismograph. Energy is up and down
movement. Vibration is perpendicular to direction
of travel. Produce continuous wriggling
motion. Do not travel through liquid.
9
SEISMIC WAVES
SURFACE WAVES
Transmit energy along Earths surface. Causes the
Earths surface to vibrate. Slowest of the
seismic waves (2.5 km/sec). Two types side to
side whipping action rolling up and down (i.e.
ocean wave) Both can occur at the same
time. Causes extensive damage to rigid structures.
10
SEISMIC WAVES
SURFACE WAVES
11
MEASURING EARTHQUAKES
MODIFIED MERCALLI INTENSITY SCALE
Earthquake strength depends on how much stored
energy is released or INTENSITY. Initially
looked at destructiveness of earthquake. Cant
locate the epicenter accurately or measure
distance and actual intensity. Doesnt
consider quality of building vs. intensity. Cant
be used where no people live. Good to
characterize historical earthquakes. Introduces a
human component to earthquakes.
12
MEASURING EARTHQUAKES
13
MEASURING EARTHQUAKES
RICHTER SCALE
Scale is based on MAGNITUDE, which is the
amount of energy released by the
earthquake. Magnitude is the amplitude of the
largest peak on the seismogram. Really designed
for use only in California. Works best for
earthquakes of magnitude 7 or less.
14
The Richter scale is logarithmic, that is an
increase of 1 magnitude unit represents a factor
of ten times in amplitude. The seismic waves
of a magnitude 6 earthquake are 10 times greater
in amplitude than those of a magnitude 5
earthquake. However, in terms of energy
release, a magnitude 6 earthquake is about 31X
greater than a magnitude 5 and 1000X greater
than a 4.
15
MEASURING EARTHQUAKES
16
MEASURING EARTHQUAKES
MOMENT-MAGNITUDE SCALE
Seismic moment more accurately gauges the total
energy of a large earthquake. MOMENT (total
length of fault rupture) X (depth of fault
rupture) X (total amount of slip along
rupture) X (strength of rock) Produces
MOMENT-MAGNITUDE scale. The longer the fault, the
greater the earthquake. Allows direct measurement
of quake related to its cause.
17
EARTHQUAKE DEPTH AND MAGNITUDE
DEPTH
Related to depth of focus of the
earthquake. Shallow focus lt 70 km (lt 45
miles) Intermediate focus 70-300 km (45-180
mi.) Deep focus gt 300 km (gt 180 miles) 90
of all earthquakes have a focus lt 100 km. Most
occur within 60 km (40 mi) of Earths
surface. Heat weakens rock with depth and rock
loses its ability to store strain energy.
18
EARTHQUAKE DEPTH AND MAGNITUDE
DEPTH
Focus closer to surface allows greater brittle
failure. 1964 Good Friday Alaskan quake D 33
km 1994 Northridge, CA quake D 21 km 1989
Loma Prieta, CA quake D 18 km
19
EARTHQUAKE DEPTH AND MAGNITUDE
MAGNITUDE
Generally, earthquakes with shallower foci have
greater magnitude. (Magnitude is the amount of
energy released by the earthquake.)
20
EFFECTS OF EARTHQUAKES
GROUND DISPLACEMENT
Most obvious geologic effect of earthquakes San
Francisco 1906 earthquake had 7 m of
horizontal displacement. Anchorage 1964 Good
Friday earthquake had land going up 12 m and
sea floor down 16 m. Anchorage earthquake was
second largest ever recorded.
21
EFFECTS OF EARTHQUAKES
GROUND DISPLACEMENT
1906 San Francisco Earthquake
1964 Anchorage Earthquake
22
(No Transcript)
23
EFFECTS OF EARTHQUAKES
LANDSLIDES AND LIQUEFACTION
Shaking and tremors dislodge unstable masses of
rocks and soil on hillsides. Fragments can be
dislodged from bedrock and buildings as well.
24
EFFECTS OF EARTHQUAKES
LANDSLIDES
1959 earthquake at Hebgen Lake, MT
1995 landslide in La Conchita, CA
25
EFFECTS OF EARTHQUAKES
FALLING DEBRIS
26
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Conversion of unconsolidated material with some
initial cohesiveness in to a mass of
water-saturated sediment that flows like a
liquid, although no water has been
added. Shaking increases the pressure on the
water between the sediment grains, forcing them
apart Loss of frictional contact produces a
slurry of sediment and mud
27
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Turnagain Heights, AK 1964
Government Hill Elementary School Anchorage, AK,
1964
28
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Kobe, Japan
29
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Kobe, Japan
30
EFFECTS OF EARTHQUAKES
LIQUEFACTION
Port Royal, Jamaica 1692 City slid 15 m below sea
level.
31
(No Transcript)