What is an temblor?
An temblor is the quiver of the Earth produced by the speedy release of energy. Most frequently. temblors are caused by motion along big breaks in the earth’s crust. Such breaks are called mistakes. The energy that is released radiates in all waies from its beginning in the signifier of moving ridges. These moving ridges are similar to the moving ridges that occur when you drop a rock into H2O. Merely as the rock sets the H2O in gesture. the energy released in an temblor produces seismal moving ridges that move through the Earth. Frequency scope of seismal moving ridges is big. from every bit high as the hearable scope ( greater than 20 Hz ) to every bit low as the frequences of the free oscillations of the whole Earth ( 2 and 7 millihertz ) . Attenuation of the moving ridges in stone imposes high-frequency bounds. and in little to chair temblors the dominant frequences extend in surface moving ridges from approximately 1 to 0. 1 Hz. The amplitude scope of seismal moving ridges is besides great in most temblors. In the greatest earthquakes the land amplitude of the prevailing P moving ridges may be several centimetres at periods of two to five seconds. Very near to the seismal beginnings of great temblors. research workers have measured big moving ridge amplitudes with accelerations of the land transcending that of gravitation ( 9. 8 metres. or 32. 2 pess. per 2nd squared ) at high frequences and land supplantings of 1 metre at low frequences.
Earthquake Magnitude and Energy Release Equivalence
What is the mechanism that produces temblors?
Earth is non a inactive planet: in the earth’s crust. tectonic forces are invariably at work forcing stones on both sides of a mistake in different waies. In this procedure. the stuff is deformed. As stones don’t slide past each other really easy. strain is built up. merely as if you bend a stick. At a certain degree. the stones can no longer defy the strain and faux pas past each other into their original form. This “springing back” of the stone is called elastic recoil. It is this speedy motion that we feel as an temblor. The elastic recoil normally happens a few kilometers deep in the crust. This location is called the focal point of the temblor. The topographic point on the surface straight over the focal point is called the epicenter.
Reid’s Elastic Rebound Theory
From an scrutiny of the supplanting of the land surface which accompanied the 1906 temblor. Henry Fielding Reid. Professor of Geology at Johns Hopkins University. concluded that the temblor must hold involved an “elastic rebound” of antecedently stored elastic emphasis. If a stretched gum elastic set is broken or cut. elastic energy stored in the gum elastic set during the stretching will all of a sudden be released. Similarly. the crust of the Earth can bit by bit hive away elastic emphasis that is released all of a sudden during an temblor.
This gradual accretion and release of emphasis and strain is now referred to as the “elastic recoil theory” of temblors. Most temblors are the consequence of the sudden elastic recoil of antecedently stored energy. The undermentioned diagram illustrates the procedure. Start at the underside. A consecutive fencing is built across the San Andreas mistake. As the Pacific home base moves north-west. it bit by bit distorts the fencing. Just before an temblor. the fencing has an “S” form. When the temblor occurs the deformation is released and the two parts of the fencing are once more consecutive ; but now there is an beginning.
Slow. Quiet and Silent Earthquakes
• When we think of an temblor beginning. we think of a cleft that propagates through the crust near to the shear-wave velocity. which is by and large several kilometres per second. Fault rupture is sudden. accompanied by violent shaking of the land. But. creep events ( on the San Andreas mistake ) during which extension along a mistake occurs at rates of millimetres per twelvemonth. Earth distortion occurs at rates that differ widely. From fast ruptures that all of a sudden let go of stored elastic-strain energy • • • • • • • Ordinary temblors to Decelerate temblors ( velocity of 100s of metres per second ) . Silent temblors ( velocity of 10s of metres per sec. ) Creep events. and eventually strive migration episodes with velocities in centimetres or millimetres per second.
Slow temblors include episodes of rupture extension that produce an ordinary seismogram of high-frequency organic structure moving ridges. However. slow temblors take an remarkably long clip to tear in comparing to ordinary temblors of similar minute magnitude. Oceanic transform mistakes have produced several slow temblors. such as the 1960 Chilean transform mistake temblor that ruptured for about an hr as a series of little events. Silent temblors are non accompanied by high-velocity rupture extension events. Therefore they do non bring forth high-frequency moving ridges that are recorded teleseismically. Conventional seismographs do non enter these events. Strain metes document creep events on the San Andreas mistake system ( 10mm/sec ) . Silent temblors may offer promise as precursors to ordinary temblors.
How can the energy of an temblor be felt?
The energy that is released in an temblor travels in moving ridges through the stuffs of the Earth. Two types of moving ridges can be distinguished. 1. Some travel along the earth’s outer bed and are called surface moving ridges. 2. Others travel through the earth’s inside and are called organic structure moving ridges. Body moving ridges are farther divided into Primary moving ridges ( P waves ) Secondary moving ridges ( S waves ) .
P moving ridges ( primary moving ridges ) P moving ridges are “push-pull” waves—they push ( compress ) and pull ( expand ) rocks in the way the moving ridge is going. Imagine keeping person by their shoulders and agitating them. This push-pull motion is how P moving ridges move through the Earth. Solids. liquids and gases resist a alteration in volume when compressed and will elastically jump back one time the force is removed. Therefore. P moving ridges can go through all these stuffs. Highest speed ( 6 km/sec in the crust ) .
S moving ridges ( secondary moving ridges )
S moving ridges. on the other manus. “shake” the atoms at right angles to their way of travel. This can be illustrated by keeping one terminal of a rope steady and agitating the other terminal ( see illustration below ) . In contrast to P moving ridges. which for a minute alteration the volume of the stuff. S waves change the form of the stuff they travel through. Because liquids and gases do non react elastically to alterations in form. they will non convey S moving ridges. An S moving ridge is slower than a P moving ridge and can merely travel through solid stone. ( 3. 6 km/sec in the crust )
Damage nature due to organic structure moving ridges
Surface Waves
Travel merely below or along the ground’s surface Slower than organic structure moving ridges ; turn overing ( Rayleigh ) and side-to-side ( Love ) motion Particularly damaging to edifices
Love Waves
After A. E. H. Love and suggested in early 20th century. L-wave can be thought of as the constructive intervention of multiple reflected S-waves whose atom gesture is horizontal. Travel merely below or along the ground’s surface with side-to-side atom speed. Speed is slower than organic structure moving ridges. This moving ridge is particularly detrimental to edifices. Typical speed: Depends on Earth construction ( diffusing ) . but less than speed of S moving ridges. Typical speed: Depends on Earth construction ( diffusing ) . but less than speed of S moving ridges. Behavior: Causes shearing gesture ( horizontal ) similar to S moving ridges. Arrival: They normally arrive after the S moving ridge and before the Rayleigh moving ridge.
Love moving ridges are diffusing. that is. different periods travel at different speeds. by and large with low frequences propagating at higher speed. Depth of incursion of the Love moving ridges is besides dependent on frequence. with lower frequences perforating to greater deepness. V L ~ 2. 0 – 4. 5 km/s in the Earth depending on frequence of the propagating moving ridge
Rayleigh Waves
After Lord Rayleigh who predicted being in 1887. These moving ridges are correspondent to moving ridges going across the ocean. A drifting object is non merely pitched up and down. but besides to and fro as wave base on ballss. The existent motion of the object describes an oval. The gesture of
moving ridges dies out rapidly with deepness. and this is besides the instance with Rayleigh moving ridges. Rayleigh moving ridge can be thought of as originating from the constructive intervention of multiple reflected P and S moving ridges going in perpendicular plane. Typical speed: ~ 0. 9 that of the S wave Behavior: Causes perpendicular ( turn overing anticlockwise ) together with back-and-forth horizontal gesture. Motion is similar to that of being in a boat in the ocean when a crestless wave moves by. Most of the agitating felt from an temblor is due to the Rayleigh moving ridge. which can be much larger than the other moving ridges. ch can be much Arrival: They normally arrive last on a seismogram.
larger than the
Rayleigh moving ridges are besides diffusing and the amplitudes by and large decrease with deepness in the Earth. Appearance and atom gesture are similar to H2O moving ridges. Depth of incursion of the Rayleigh moving ridges is besides dependent on frequence. with lower frequences perforating to greater deepness. Generally. Rayleigh waves travel somewhat slower than Love moving ridges. VR ~ 2. 0 – 4. 5 km/s in the Earth depending on frequence of the propagating moving ridge
Damage form due to come up moving ridges
What is a seismograph and how does it work?
A seismograph is an instrument that records temblor moving ridges ( besides called seismal moving ridges ) . The rule: A weight is freely suspended from a support that is attached to bedrock. When moving ridges from an temblor reach the instrument. the inactiveness of the weight keeps it stationary. while the Earth and the support vibrate. The motion of the Earth in relation to the stationary weight is recorded on a rotating membranophone. What is recorded on the revolving membranophone is called a seismogram.
Seismograms show that there are two types of seismal moving ridges generated by the
motion of a mass of stone.
Example of an temblor record.
Locating an Earthquake’s Epicenter
P moving ridges arrive foremost. so S moving ridges. so L and R After an temblor. the difference in arrival times at a seismograph station can be used to cipher the distance from the seismograph to the temblor beginning ( D ) . If mean velocities for all these moving ridges are known. utilize the S-P ( S minus P ) clip expression: a method to calculate the distance ( D ) between a recording station and an event. Distance Time = Velocity P moving ridge has a speed VP and S wave has a speed VS ; VS is less than VP Both originate at the same topographic point – the hypocenter They travel same distance. but the S wave takes more clip than the P moving ridge. D Time for the S wave to go a distance DTS = Vs D Time for the P wave to go a distance DTP = Vp The clip difference ( TS – TP ) = D D =D Vs Vp
? 1 1 ? ? ? Vs – Vp ? = D ? ? ?
? Vp – Vs ? ? ? Vp Vs ? ? ? ?
Now work out for the Distance D
? Vp Vs ? D= ? ? Vp – Vs ? * ( TS – TP ) ? ? ?
Epicenter of an temblor can be obtained by surface projection of temblor beginning. Travel-times for location
Measure clip between P and S wave on seismogram Use travel-time graph to acquire distance to epicenter
The epicentre is located utilizing three or more seismograph
Earthquake deepnesss
? Earthquakes originate at deepnesss runing from 5 to about 700 kilometres ? Earthquake focal point classified as ? Shallow ( surface to 70 kilometres ) ? Intermediate ( 70 to 300 kilometres ) ? Deep ( over 300 kilometres )
Seismic Wave Speeds and Rock Properties
Variations in the velocity at which seismal moving ridges propagate through the Earth can do fluctuations in seismal moving ridges recorded at the Earth’s surface
Vp =
?4 ? ? µ + k? ?3 ?
?
Vs =
µ ?
It can be shown that in homogenous. isotropous media the speeds of P and S waves through the media are given by the looks as above. Where Vp and Vs are the P and S wave speeds of the medium. ? is the denseness of the medium. and µ and Ks are referred to as the shear and majority moduli of the media. Taken together. µ and K are besides known as elastic parametric quantities. The elastic parametric quantities quantitatively describe the undermentioned physical features of the medium. •
Bulk Modulus – Is besides known as the incompressibility of the medium. The majority modulus describes the ratio of the force per unit area applied to the regular hexahedron to the sum of volume alteration that the regular hexahedron undergoes. If K is really big. so the stuff is really stiff. significance that it doesn’t compress really much even under big force per unit areas. If K is little. so a little force per unit area can compact the stuff by big sums. For illustration. gases have really little incompressibilities. Solids and liquids have big incompressibilities. Shear Modulus – The shear modulus describes how hard it is to deform a regular hexahedron of the stuff under an applied shearing force. For illustration. imagine you have a regular hexahedron of stuff steadfastly cemented to a table top. Now. push on one of the top borders of the stuff analogue to the tabular array top. If the stuff has a little shear modulus. you will be able to deform the regular hexahedron in the way you are forcing it so that the regular hexahedron will take on the form of a parallelogram. If the stuff has a big shear modulus. it will take a big force applied in this way to deform the regular hexahedron. Gass and fluids can non back up shear forces. That is. they have shear moduli of nothing. From the equations given supra. notice that this implies that fluids and gases do non let the extension of S moving ridges.
Any alteration in stone or dirt belongings that causes ?. µ. or K to alter will do seismal moving ridge velocity to alter. For illustration. traveling from an unsaturated dirt to a saturated dirt will do both the denseness and the majority modulus to alter. The majority modulus alterations because air-filled pores go filled with H2O. Water is much more hard to compact than air. In fact. majority modulus alterations dominate this illustration. Therefore. the P wave speed changes a batch across H2O tabular array while S wave speeds change really small.
Wave Propagation Through Earth Media
? Any alteration in stone or dirt belongings that causes ?. µ. or K to alter will do seismal moving ridge velocity to alter. ? For illustration. traveling from an unsaturated dirt to a saturated dirt will do both the denseness and the majority modulus to alter. ? When seismal moving ridges travel from one bed to another. beam gets dead set off from or toward the normal depending on bed denseness. ? Propagation of seismal moving ridges in media is governed by Snell’s Law Snell’s Law describes the relationship between the angles and the speeds of the moving ridges. Snell’s jurisprudence equates the ratio of stuff speeds V1 and V2 to the ratio of the sine’s of incident and refracted angles. as shown in the undermentioned equation.
wickedness ?1 wickedness ?2 = VL1 VL 2
Where: VL1 is the longitudinal moving ridge speed in stuff 1. VL2 is the longitudinal moving ridge speed in stuff 2.
Shows P and S wave shadow zones that forms on other side of the Earth due to the happening of an temblor in opposite side.
P – P wave merely in the mantle PP. PPP. SS. SSS – P or S wave reflected one time or twice off earth’s surface so there are two or more Phosphoruss or S wave sections in the mantle. PKP – P wave that has two sections in the mantle separated by a section in the nucleus. PcP – P wave reflected from outer nucleus & A ; mantle boundary. PKiKP – P wave reflected from outer nucleus & A ; inner nucleus boundary. PKIKP – P wave that crossbeam inner nucleus is denoted by I. PKJKP – Phases with an S leg in the inner nucleus is denoted by J. PPS. PSP. PSS – P beckon twice reflected from the Earth’s surface. S denotes converted moving ridge.
ScP – S wave reflected from outer core-mantle boundary and converted into P type moving ridge. ScS – S wave reflected from outer nucleus & A ; mantle boundary. SKS – S wave tracking the outer nucleus as P and converted back into S when once more come ining the mantle.
Earth’s Major Boundaries
The crust – Continental » Less heavy » 20-70 kilometer midst – Oceanic » more heavy » 5-10 kilometer midst
The ( Moho ) Mohorovicic discontinuity
Discovered in 1909 by Andriaja Mohorovicic Separates crustal stuffs from underlying mantle Identified by a alteration in the speed of P moving ridges
• The core-mantle boundary
• • Discovered in 1914 by Beno Gutenberg Based on the observation that P waves decease out at 105 grades from the temblor and reappear at about 140 grades • 35 degree broad belt is named the P-wave shadow zone
• Discovery of the inner nucleus
• • Predicted by Inge Lehmann in 1936 P-wave shadow zone is non a perfect shadow – there are weak Pwaves geting. and Lehmann suggested that these P-waves were bounced from a solid inner nucleus.
Foreshocks and Aftershocks
Mistakes are believed to dwell of stronger and weaker parts whose ability to tear during an temblor varies. These stronger parts are called barriers or grimnesss. These two footings assign different functions to the stronger spots in the temblor rupture procedure.
The left side of the above figure shows the status of a mistake merely before an temblor while the right side shows its status after an temblor. The upper portion of the figure is based on the barrier hypothesis. while the lower portion is based on the grimness hypothesis. The shaded part indicates a stressed part of the mistake while the unshaded is the slipped or unstressed part. Harmonizing to the barrier hypothesis. the mistake is in a province of unvarying emphasis ( upper left ) before the temblor. During the temblor the rupture propagates go forthing unbroken stronger spots ( upper right ) . These spots or barriers are the location of legion aftershocks which represent the release of emphasis through inactive weariness. Harmonizing to the grimness hypothesis. merely prior to the temblor ( chief daze ) the mistake is non in a province of unvarying emphasis but instead there has been some release of emphasis over portion of the mistake through foreshocks go forthing behind strong spots or grimnesss which are broken ensuing in a smoothly slipped mistake ( lower right ) . The being of both aftershocks and foreshocks indicate that some strong spots behave as barriers while others behave as grimnesss. Barriers and grimnesss are important to temblor land gesture because they represent locations of concentrated emphasis release and localised fillet and starting of the rupturing mistake.
Measuring the size of temblors
Two measurings that describe the size of an temblor are • • • Intensity – a step of the grade of temblor shaking at a given venue based on the sum of harm Magnitude – estimates the sum of energy released at the beginning of the temblor The drawback of strength graduated tables is that devastation may non be a true step of the temblors existent badness
The Modified Mercalli ( MM ) Scale of Earthquake Intensity ( Developed in 1931 by the American seismologists Harry Wood and Frank Neuman ) Intensity I II III IV Felt / Damage People do non experience any Earth motion. A few people might detect motion if they are at rest and/or on the upper floors of tall edifices. Many people indoors feel motion. Hanging objects swing back and Forth. Peoples out-of-doorss might non recognize that an temblor is happening. Most people indoors feel motion. Hanging objects swing. Dishes. Windowss. and doors rattle. The temblor feels like a heavy truck hitting the walls. A few people out-of-doorss may experience motion. Parked autos stone. Almost everyone feels motion. Sleeping people are awakened. Doors swing unfastened or close. Dishs are broken. Pictures on the wall move. Small objects move or are turned over. Trees might agitate. Liquids might slop out of unfastened containers. Everyone feels motion. Peoples have problem walking. Objects fall from shelves. Pictures fall off walls. Furniture moves. Plaster in walls might check. Trees and shrubs shake. Damage is slight in ill built edifices. No structural harm. Peoples have trouble standing. Drivers feel their autos agitating. Some furniture interruptions. Loose bricks fall from edifices.
Damage is little to chair in well-built edifices ; considerable in ill built edifices. Drivers have problem guidance. Houses that are non bolted down might switch on their foundations. Tall constructions such as towers and chimneys might writhe and fall. Well-built edifices suffer little harm. Ill built constructions suffer terrible harm. Tree subdivisions break. Hillsides might check if the land is wet. Water degrees in Wellss might alter. Well-built edifices suffer considerable harm. Houses that are non bolted down travel off their foundations. Some belowground pipes are broken. The land clefts. Reservoirs suffer serious harm. Most edifices and their foundations are destroyed. Some Bridgess are destroyed. Dams are earnestly damaged. Large landslides occur. Water is thrown on the Bankss of canals. rivers. lakes. The land cracks in big countries. Railway paths are dead set somewhat. Most edifices prostration. Some Bridgess are destroyed. Large clefts appear in the land. Underground grapevines are destroyed. Railway paths are severely dead set. Almost everything is destroyed. Objects are thrown into the air. The land moves in moving ridges or ripplings. Large sums of stone may travel.
Magnitude
Magnitude of temblor is a step of energy and based on the amplitude of the moving ridges recorded on a seismogram. Concept: the moving ridge amplitude reflects the temblor size once the amplitudes are corrected for the lessening with distance due to geometric spreading and fading. Magnitude graduated tables have the general signifier:
where A: amplitude of the signal Thymine: its dominant period degree Fahrenheit: rectification for the fluctuation of amplitude with the earthquake’s deepness H and distance ? from the seismometer C: regional graduated table factor
Richter Magnitude
Charles Richter developed the first magnitude graduated table in 1935. Richter’s magnitude is the logarithm to the base 10 of the maximal seismal moving ridge amplitude. in thousandths of a millimetre. recorded on a particular type of seismograph ( Wood-Anderson seismograph ) at a distance of 100 kilometer from the temblor epicentre. Wood-Anderson seismograph has a natural oscillation period of about 0. 8 seconds. and moving ridges of longer period are progressively diminished on the records even if they are present in the land.
ML = log10A ( millimeter ) + ( Distance rectification factor )
Here A is the amplitude. in millimetres. measured straight from the photographic paper record of the Wood-Anderson seismometer. a particular type of instrument. He proposed zero magnitude for an temblor that would bring forth a record with amplitude of 1. 0 micro metre at a distance of 100 kilometer from the epicentre on WoodAnderson seismograph with clip period 0. 8 sec ( 1. 25 Hz natural frequence ) . muffling h 0. 8 and 2800 magnification factor. He calibrated his graduated table of magnitudes utilizing measured maximal amplitudes of shear moving ridges recorded in southern California. The logarithmic signifier of Richter magnitude graduated table ( ML ) for 100 km epicentral distance is as given below.
ML = log10A – log10A0
Where. A0 is the amplitude for zero magnitude temblors. Therefore. an temblor hint with amplitude 10 micro metre of seismograph at an epicentral distance of 100 kilometer has magnitude 1. 0
The distance factor by Richter
The diagram below demonstrates how to utilize Richter’s original method to mensurate a seismogram for a magnitude estimation in Southern California:
The graduated tables in the diagram above signifier a nomograph that allows you to make the mathematical calculation rapidly by oculus.
Body-wave magnitude is
Mb = log ( A/T ) + Q ( D. H )
where A is the land gesture ( in micrometers ) . T is the wave’s period ( in seconds ) . and Q ( D. H ) is a rectification factor that depends on distance to the quake’s epicentre D ( in grades ) and focal deepness H ( in kilometres ) . Mb uses comparatively short seismal moving ridges with a 1-second period. so to it every temblor beginning that is larger than a few wavelengths looks the same. Mb saturates around magnitude above 6.
Surface-wave magnitude is
Ms = log ( A/T ) + 1. 66 logD + 3. 30
Ms uses 20-second moving ridges and can manage larger beginnings. but it excessively saturates around magnitude 8. That’s OK for most intents because magnitude-8 or great events go on merely approximately one time a twelvemonth on norm for the whole planet. But within their bounds. these two graduated tables are a dependable gage of the existent energy that earthquakes release. Restrictions: Magnitude impregnation It’s a general phenomenon for Mb above approximately 6. 2 and Ms above approximately 8. 3.
A simple solution that has been found by Kanamori: specifying a magnitude graduated table based on the seismal minute. Moment Magnitude. Mw. is non based on seismometer readings at all but on the entire energy released in a temblor. the seismal minute Mo ( in dyne-centimeters ) :
Mw = 2/3 log ( Mo ) – 10. 7
This graduated table therefore does non saturate. Moment magnitude can fit anything the Earth can throw at us. Still. Kanamori inserted an accommodation in his expression such that below magnitude 8 Mw lucifers Ms and below magnitude 6 lucifers Mb. which is near adequate to Richter’s old ML. So keep naming it the Richter graduated table if you like—it’s the graduated table Richter would hold made if he could. Seismic Moment ( Mo ) = The seismal minute is a step of the size of an temblor based on the country of mistake rupture. the mean sum of faux pas. and the force that was required to get the better of the clash lodging the stones together that were offset by blaming.
Moment = µ A D µ = shear modulus ; A = LW = country D = mean supplanting during rupture
Land Motion Acceleration Measurement
Peak land acceleration ( PGA ) is a step of temblor acceleration. Unlike the Richter magnitude graduated table. it is non a step of the entire size of the temblor. but instead how difficult the Earth shakes in a given geographic country. It is measured by instruments. non from personal studies. although it by and large correlates good with the Mercalli graduated table.
Peak land acceleration can be measured in g ( the acceleration due to gravitation ) or m/s? . The peak horizontal acceleration ( PHA ) is the most
normally used type of land acceleration in technology applications. Other land gesture parametric quantities used to qualify temblor gesture include peak speed and peak supplanting.
Strong Gesture Detectors
Most strong gesture detectors are designed to mensurate the big amplitude. high frequence seismal waves typical of big local temblors. These seismal moving ridges result in the strong land gesture we feel during a big temblor. Strong land gesture is frequently to fault for the structural harm that occurs during an temblor. The information seismologists record with strong gesture detectors is used to better the design of temblor immune edifices and to understand earthquake-induced geologic jeopardies like liquefaction and landslides. The scope of gestures of involvement for strong gesture applications includes accelerations from 0. 001 to 2 g and frequences from 0 to 100 Hz.
Why We Need Strong Motion Detectors
Before the broad usage of strong gesture instruments. scientists attempted to gauge the shaking from strong temblors by generalizing ( scaling up ) the ascertained effects of smaller temblors ( magnitude 2. 5-5. 0 ) . This method works good for many applications and has improved with the usage of informations from strong gesture instruments. However. this attack is non applicable in every state of affairs. Some geologic stuffs and constructions do non react to strong shaking in a simple. predictable mode that can be accurately scaly upward. In these state of affairss. scientists need existent informations generated by strong land gesture to better understand the procedures at work. Strong gesture detectors have been installed in different countries of geologic involvement throughout the Pacific Northwest to supply this type of informations. Using strong gesture informations. Earth scientists hope to derive a better apprehension of: 1 ) land response near mistake ruptures of big temblors 2 ) effects of terrible agitating on different subsurface constructions and geologic stuffs. 3 ) land response in countries that undergo liquefaction.
