Earthquake Engineering 2012 Lecture 0102 Nature of Earthquakes

EARTHQUAKEEARTHQUAKE

N f N f

EARTHQUAKEEARTHQUAKEENGINEERINGENGINEERING

11..22. Nature of . Nature of EarthquakesEarthquakes

11..22..11. Causes of Earthquakes. Causes of Earthquakes

11..22..22. Faults. Faults

1.2.3. Earthquake Effects1.2.3. Earthquake Effects

1.2.1. Causes of Earthquakes

Tectonic EarthquakesTectonic Earthquakesare caused by the sudden dislocation of large rock masses alonggeological faultsfaults within the earth's crust. The Earth is formed of

l l h h diff h i l d h i l

Tectonic EarthquakesTectonic Earthquakes

several layers that have very different physical and chemicalproperties. The outer layer, which averages about 70 kilometersin thickness, consists of about a dozen large, irregularly shapedplates that slide over under and past each other on top of theplates that slide over, under and past each other on top of thepartly molten inner layer . MostMost earthquakesearthquakes occuroccur atat thetheboundariesboundaries wherewhere thethe platesplates meetmeet ..

Plate Tectonic InteractionsFlash movie

Dr. Osman Shalan Dr. Tharwat Sakr


Tectonic EarthquakesTectonic EarthquakesTectonic EarthquakesTectonic Earthquakes



Volcanic EarthquakesVolcanic Earthquakes

Earthquakes that can bereasonably associated with

Volcanic EarthquakesVolcanic Earthquakes

reasonably associated withvolcanoes are relatively rareand fall into three categories:

(i) volcanic explosions,

(ii) shallow earthquakes from(ii) shallow earthquakes frommagma movements, and

(iii) sympathetic tectonic(iii) sympathetic tectonicearthquakes



Volcanic EarthquakesVolcanic EarthquakesVolcanic EarthquakesVolcanic Earthquakes



Volcanic EarthquakesVolcanic EarthquakesVolcanic EarthquakesVolcanic Earthquakes

Dr. Osman Shaalan Dr. Tharwat Sakr


ExplosionsExplosions

Earthquakes may be produced

ExplosionsExplosions

q y pby the undergrounddetonation of chemical ornuclear devices When anuclear devices. When anuclear device is detonated ina borehole underground,enormous nuclear energy isreleased .



Collapse EarthquakesCollapse EarthquakesCollapse EarthquakesCollapse Earthquakes

Collapse earthquakes are small earthquakes occur inregions of underground caverns and mines. The immediatecause of ground shaking is the sudden collapse of the roofg g pof the mine or cavern.



Large ReservoirLarge Reservoir induced Earthquakesinduced EarthquakesLarge ReservoirLarge Reservoir--induced Earthquakesinduced Earthquakes

The idea that earthquakes might be triggered by impoundingq g gg y p gsurface water is not new. The first detailed evidence of such aneffect came with the filling of Lake Mead behind Hoover Dam(height 221 m. After impounding began , reports of local shakingb l tbecame prevalent.



TsunamiTsunamiTsunamiTsunamiUnderwater earthquakes,volcanoes, or landslidescan produce a tsunami orcan produce a tsunami ortidal wave. This wave cantravel very rapidlythousands of miles acrossthe ocean. In deep waterthe tsunami may only raisethe ocean level by a fewcentimeters hardly enoughcentimeters, hardly enoughto notice. But as itapproaches land, theshallower water causes theshallower water causes thewave to build in height toas much as 10-20 metersor more and suddenly


flood coastal areas

1.2.2. Faults

DefinitionDefinitionAA faultfault is a fracture within someparticular rocky mass within the

h' Th d h d

DefinitionDefinition

earth's crust. The depth andlength of faults vary greatly.Faults may range in length fromfew meters to many kilometersfew meters to many kilometersand are drawn on a geologicalmap as continuous or brokenlines. Earthquakes are caused byq yactiveactive faultsfaults, that is, faults alongwhich the two sides of thefracture move with respect to

h th S th k ieach other. So, an earthquake iscaused by the sudden movementof the two sides of a fault withrespect to anotherrespect to another .


1.2.2. Faults

Active FaultsActive FaultsActive FaultsActive Faults

Prof.Dr. Osman Shaalan Dr. Tharwat Sakr

1.2.2. Faults

Tectonic PlatesTectonic PlatesTectonic PlatesTectonic Plates


1.2.2. Faults

Types of FaultsTypes of Faults a)a) NormalNormal faultsfaultsThese occur in response to pulling

i h l i bl k

Types of FaultsTypes of Faults

or tension: the overlying blockmoves down the dip of the faultplane. movieb)b) ThrustThrust (reverse)(reverse) faultsfaultsb)b) ThrustThrust (reverse)(reverse) faultsfaultsThese occur in response tosqueezing or compression: theoverlying block moves up the dipy g p pof the fault plane. moviec)c) StrikeStrike‐‐slipslip (lateral)(lateral) faultsfaultsThese occur in response to eithert f t th bl ktype of stress: the blocks movehorizontally past one another . movie

Prof.Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sakr

1.2.2. Faults

Earthquake FocusEarthquake FocusEarthquake FocusEarthquake FocusThe point on the fault whererupture initiates is referred to

h ff h th tas the focusfocus or hypocenterhypocenterof an earthquake.

The hypocenterhypocenter of anearthquake is described byq yits depth in kilometers, itsmap location in latitude andlongitude, its date and timef d i

The term epicenterepicenter is thepoint on the earth’s surfaceof occurrence, and its

magnitudepoint on the earth s surfacedirectly above thehypocenterhypocenter

Prof. Dr. Osman Shaalan Earthquake Engineering Dr. Tharwat Sak

1.2.3. Earthquake Effects

How do Earthquakes affect Structures?How do Earthquakes affect Structures?

1‐ By inertial forcesd b

qq

generated by severeground shaking

Overturning collapse of a high-rise building Chi-Chi earthquake, Taiwan, September 20,Chi Chi earthquake, Taiwan, September 20,

1999, Magnitude 7.6



How do Earthquakes affect Structures?How do Earthquakes affect Structures?

2. By earthquake‐i d d fi

qq

induced fires:

Damage caused by the earthquake induced fires Hanshin (Kobe) earthquake, January 17, 1995, Japan,Hanshin (Kobe) earthquake, January 17, 1995, Japan,

Magnitude 6.9



How do Earthquakes affect Structures?How do Earthquakes affect Structures?3. By changing the physical properties of the foundation soils such as

Liquefaction:

qq

Damage due to liquefactionOverturning due to liquefaction Damage due to liquefaction1964 Niigata, Japan, earthquake.

g qKocaeli earthquake, Turkey, 1999, Magnitude 7.4



How do Earthquakes affect Structures?How do Earthquakes affect Structures?qq



How do Earthquakes affect Structures?How do Earthquakes affect Structures?4. By direct fault displacement at the site of a structure:

qq



How do Earthquakes affect Structures?How do Earthquakes affect Structures?5. By landslides, or other movement:

qq



How do Earthquakes affect Structures?How do Earthquakes affect Structures?6. By seismic sea waves (tsunamis) or fluid motions in

reservoirs and lakes (seiches):

qq


Earthquake Engineering 2012 Lecture 0102 Nature of Earthquakes

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