SEISMIC WAVES

SEISMIC WAVES

            Earthquakes produce vibrations called seismic waves, moving from the focus outward in all directions. Just like sound waves, these waves get weaker as they move away from the focus. This means, the farther you go from the hypocenter, the weaker the earthquake becomes.

TWO KINDS OF SEISMIC WAVES:

1.      BODY WAVES= very fast seismic waves moving through or inside the earth. These cause the most damage.

TWO TYPES OF BODY WAVES:

A.     Primary ( P ) or compressional waves = push and pull of the rocks in the earth. These can pass through solids, liquids and gases. They cause buildings to expand and contract ( compress). They move faster than shear waves.

B.      Secondary ( S) or Shear waves = move the rocks from side to side. They can only pass through solids. They cause buildings to shake.

2.      SURFACE WAVES = very slow, long waves moving along the earth’s surface, causing rocking movements that cause little damage to structures.

Two types of surface waves:

A.     Love waves = horizontally move along the surface, causing a side-to-side movement. This was named after Augustus E. H. Love, a British physicist who discovered it in 1911.

B.       Rayleigh waves = causes the surface to roll like the wave of the ocean, named after Lord Rayleigh, who discovered it in 1885.

Table 1.  Main types of seismic waves.
wave type	particle motion	name
body waves	longitudinal	P wave
	transverse	S wave
surface waves	horizontal transverse	Love wave
	vertical elliptical	Rayleigh wave

Animated seismic waves =  p & s waves

http://neic.usgs.gov/neis/eq_depot/2002/eq_021103/ak_seismic_waves.html

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm

love and Rayleigh waves

http://seismo.berkeley.edu/blogs/seismoblog.php/2009/07/27/title-5

http://www.geo.mtu.edu/UPSeis/waves.html

seismic waves http://www-rohan.sdsu.edu/~rmellors/lab8/l8maineq.htm

EARTHQUAKE TERMS

EARTHQUAKE=  vibration of the Earth due to the rapid release of energy.

The process by which rocks bend, store and suddenly release energy is described in the elastic rebound theory.

It was proposed by HARRY F. REID of Hopkins University as the mechanism for the generation of earthquakes. Reid came up with the idea after the occurrence of the terrible San Francisco earthquake in California, U.S.A. in 1906.

FOCUS/ HYPOCENTER= exact center of the earthquake below the earth’s surface.

 EPICENTER= point above the focus

FOCAL DEPTH= depth of the focus (70-700km down)

·         Amplification

Shaking levels at a site may be increased, or amplified, by focusing of seismic energy caused by the geometry of the sediment velocity structure, such as basin subsurface topography, or by surface topography.

·         Asperity

An asperity is an area on a fault that is stuck. The earthquake rupture usually begins at an asperity.

·         Attenuation

When you throw a pebble in a pond, it makes waves on the surface that move out from the place where the pebble entered the water. The waves are largest where they are formed and gradually get smaller as they move away. This decrease in size, or amplitude, of the waves is called attenuation. Seismic waves also become attenuated as they move away from the earthquake source.

·         Blind Thrust Fault

A thrust fault that does not rupture all the way up to the surface so there is no evidence of it on the ground. It is "buried" under the uppermost layers of rock in the crust.

·         Directivity

Directivity is an effect of a fault rupturing whereby earthquake ground motion in the direction of rupture propagation is more severe than that in other directions from the earthquake source.

·         Divergent Boundary

A divergent boundary is where two adjacent tectonic plates are moving away from each other.

·         Elastic Rebound

Elastic rebound is what happens to the crustal material on either side of a fault during an earthquake. The idea is that a fault is stuck until the strain accumulated in the rock on either side of the fault has overcome the friction making it stick. The rock becomes distorted, or bent, but holds its position until the earthquake occurs, and the rock snaps back into an unstrained position, releasing energy that produces seismic waves.

·         Foreshocks

Foreshocks are relatively smaller earthquakes that precede the largest earthquake in a series, which is termed the mainshock. Not all mainshocks have foreshocks. Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over a period of weeks, months, or years. In general, the larger the mainshock, the larger and more numerous the aftershocks, and the longer they will continue.

·         Horst & Graben

A horst is an upthrown block lying between two steep-angled fault blocks. A graben is a down-dropped block of the earth's crust resulting from extension, or pulling, of the crust.

·         Great Circles

The shortest path between two points on the surface of a sphere lies along a great circle.

·         Liquefaction

A process by which water-saturated sediment temporarily loses strength and acts as a fluid, like when you wiggle your toes in the wet sand near the water at the beach. This effect can be caused by earthquake shaking.

·         Normal Fault

Dip-slip faults are inclined fractures where the blocks have mostly shifted vertically. If the rock mass above an inclined fault moves down, the fault is termed normal, whereas if the rock above the fault moves up, the fault is termed reverse.

·         Shadow Zone

The shadow zone is the area of the earth from angular distances of 104 to 140 degrees that, for a given earthquake, does not receive any direct P waves. The shadow zone results from S waves (not shown in animation) being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

·         Strike-Slip Fault

Strike-slip faults are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right lateral; if the block moves to the left, the motion is termed left lateral.

·         Thrust Fault

A thrust fault is a reverse fault with a dip of 45� or less.

·         Wavefront

The wavefront is the instantaneous boundary between the seismic waves in the earth material, and the material that the seismic energy has not yet reached.

STRUCTURE OF THE EARTH

·         The three main layers of Earth: crust (outermost, rigid, very thin, brittle), mantle (dense, hot layer of semi-solid rock), and core (nearly twice as dense as the mantle because its composition is metallic – iron-nickel alloy, made up of liquid outer core and a solid inner core).

·         Lithosphere is the rigid outer part of the earth composed of the crust and the upper mantle.

·         Asthenosphere - lies below the lithosphere, relatively narrow, mobile zone in the mantle, composed of hot, semi-solid material, which can soften and flow after being subjected to high temperature and pressure over geologic time. The rigid lithosphere is thought to "float" or move about on the slowly flowing asthenosphere

·         In geologic terms, a plate is a large, rigid slab of solid rock. Plate tectonics, refers to how the Earth's surface is built of plates. The Earth’s crust is made up of 16 some are big like the North American plate and others are small like the Philippine plate.

·         The Continental Drift hypothesis proposes that the continents were once joined in a large continent, Pangaea. This supercontinent split apart and the continents drifted to their present positions. This theory is the forerunner to the theory of plate tectonics.

·         The Seafloor Spreading hypothesis proposes that the seafloor is in motion caused by the movement in the mantle beneath the seafloor.

·         The Theory of Plate Tectonics states that the Earth's outermost layer is fragmented into a dozen or more, large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. 

REFERENCE WEBSITES ( Plate Tectonics)

Interactive activities

Here are my favorite sites for this topic  “ plates and boundaries”.

plates&boundarieshttp://www.learner.org/interactives/dynamicearth/plate2.html

Plates on the move http://www.amnh.org/ology/index.php?channel=earth#features/plates?TB_iframe=true&height=500&width=750

http://science.pppst.com/platetectonics.html

http://msteacher.org/epubs/science/science1/activities.aspx

plate tectonics  http://science.pppst.com/platetectonics.html

interactive dynamic earth http://www.learner.org/interactives/dynamicearth/structure.html

plate and boundaries http://www.learner.org/interactives/dynamicearth/plate.html

MIDDLE SCHOOL PORTALhttp://msteacher.org/epubs/science/science1/activities.aspx

LABORATORY SYMBOL AND SAFETY DEVICES

Lesson: LABORATORY SYMBOL AND   SAFETY      DEVICES

1. SUBJECT NAME: INTEGRATED SCIENCE

    B.LESSON REFERENCE NUMBER: 6

    C. LESSON TITLE: SAFETY PRECAUTIONS IN THE LABORATORY

    D. LESSON DESCRIPTION:

            At the end of the activities, the students should be able:

1.        identify standard safety symbols and devices in the laboratory;

2.        explain the significance of the symbols and devices in doing laboratory work.; 

3.        design laboratory safety symbols;

4.        develop creativity in group work;

5.        show  awareness, vigilance, presence of mind and self-discipline.

 

    E. REVIEW OF PREVIOUS LEARNING LESSON:

                        Sample apparatus, their uses and classification

Apparatus	Uses/Function	Basis of Classification
1.  Balance, set of weights 2.  Graduated cylinder 3.  Thermometer 4.  Alcohol burner/Bunsen burner 5.  Flask, beakers, test tubes 6.  Reagent bottles	measure mass measure volume measures temperature heat substance/mixture container for liquids container for liquids	measuring measuring measuring heating handling liquids storing solids and liquids

                  

    G. LEARNING PRESENTATION:

          http://www.baruch.cuny.edu/tutorials/weissman/chemlab/Template.html

    H. LEARNING ACTIVITY:

          http://designsuperhighway.com/Flash/flash_files/labsafety.html

        

Safety precautions in the laboratory.  (adopted from Integrated Science I by Villamil and Science and Technology I by Lianko).

o   Think in terms of safe practices at all times.

o   Be familiar with every step you do.

o   Act promptly and calmly when confronted with an emergency.  A first aid kit should always be available.

o   Check the apparatus, item and chemical at least twice before use.  Glass apparatus should be handled with care.

o   Volatile and inflammable liquids should be kept away from open flames so as to avoid burns and fires.

o   Valves of heating devices should be properly closed         when not in use to avoid over heating.

o   Measuring scales should likewise be handled properly so as not to affect their accuracy and equilibrium.

o   Handling solid substances, heating test tubes, and filtering substances in the laboratory should also be done properly.

I.           LEARNING EVALUATION

1.         Locate and encircle some safety devices and materials  in the puzzle below:

II.             

G	P	A	I	L	O	F	S	A	N	D
T	O	N	I	C	F	A	L	S	E	O
P	A	O	S	W	A	T	E	R	V	O
B	A	R	G	B	U	R	N	S	E	H
N	A	P	L	L	C	A	C	U	R	E
R	I	A	O	W	E	A	R	M	O	M
S	T	O	V	A	T	S	A	A	M	U
X	I	C	E	I	K	N	I	S	G	F
F	I	R	S	T	A	I	D	K	I	T

2.   The following are safety devices usually found in laboratories. Fill in the missing letters and identify the device.

•       a.  __o__gl__s                                               - eye protector
•       b.  g__ov__s                                                 - protect your hands
•       c.  F__r__E__ti__ __ ui__h__r                  - put off flame
•       d.  __ir__t  A__d  _it                                     - contains medicines
•       e.  L__b__ __at__r__  A__r__n                  - body protector
•