Unit 1

Hypocenter or focus: point at which the slip of an earthquake begins. Hypocenters are therefore always located at some depth underground.From there, body seismic waves(ondas profundas) [primary waves (P) and secondary waves (S)] spread in alldirections in spherical wavefronts.

Epicenter: An epicenter has no physical meaning; it is simply the point on the Earth's surface directly above the hypocenter. From there, surfaceseismic waves (ondas sísmicas superficiales) are released [Rayleighwaves (R) and Love waves (L)], theones causing damages.

Earthquakes elements

Study of the Earth’s interior

Hypocenter

Epicenter

Study of the Earth’s interior

They are originated from the epicentre, and spread over the surface.

Vibrations originated in the hypocentre, theytravel through the inner layers of the Earth.

WAVES

BODY W.

SURFACE W.

•Primary or Pressure waves P (ondas primarias o longitudinales): the fastest ones.•There are areas of compression and expansion, following the same direction as the wave movement.• Through solid and liquid materials.

•Secondary waves S (ondas secudnarias o transversales): slower than P waves.•Oscillations are at right angles to the direction of travel. •Through solid materials.

• They are slower than the body waves.•They cause most of the catastrophic effects in structures, buildings and also cause tsunamis.

Primary W. (P)

Secondary W. (S)

Rayleigh R & Love L W.

Study of the Earth’s interior

Estructura de la geosfera

Models

Geochemical

Geodynamic

Analyzes the geosphere’s structure according to its chemical composition of its layers.

Analyzes the geosphere’s structureaccording to the mechanical behaviour of its materials.

Both models studies composition and distribution of materials in the Earth. Both consider the geosphere

a set of concentrical layers.

To study these structure and composition, we use indirect methods, as we can’t access the inner layers: the seismic method, gravimetric methods.It is also possible to use direct methods, like magma analisis and crust explorations (drilling).

Study of the Earth’s interior

Geochemical model

10-70km

700km

2900km

10-70km

Geochemical model

Layer CharacteristicsCrust Continental Less dense. Granite. Older. 25-70km thick.

Oceanic Denser. Basalt. Newer. Less than 10km thick.

Mohorovicic discontinuity 10-70km

Mantle(60%)

Upper Plastic rocks (“reid”). Less dense the the lower one.

Repetti discontinuity 670km

Lower Plastic rocks (“reid”). Denser than the upper one.

Gutenberg discontinuity 2900km

Core(30%)

Outer Liquid, its movement generates the magnetosphere.

Lehman discontinuity 5150km

Inner Solid due to the high pressure.

Geochemical model

Geodynamic model

Modelo DINÁMICO

Astenosphere: Nowadays, according to recent studies, the asthenosphere IS NOT A CONTINUOUS LAYER. It is conformed by specific plastic regions of the upper mantle.

Lithosphere: It’sdivided into plates.

LITHOSPHERE

ASTENOSPHERE

MESOSPHERE

D LAYER

OUTER CORE

INNERCORE

•What is a

discontinuity? How

many discontinuities

do you observe?

Where are they?

• Is it a homogeneus

or heterogeneus

internal structure?

Explain your answer.

•How many layers

are there? Describe

their structure and

states of matter.

1. The following figure represents the seismic waves velocity, in

an imaginary planet. Answer the questions:

Create a Venn’s-Diagram about the oceanic and the continental crust. Use the information given.

LESS DENSEDENSERGRANITE.BASALT.THICKER.THINNER.ON MANTLE.OLDER.YOUNGER.PART OF THE LITHOSPHERE.SOLID.

Oceaniccrust

Continental crust

Both

The internal engine of the Earth

The lithosphere floats

on top of the

sublifthospheric

mantle, in a state of

ISOSTASY (isostasia).

The internal and

external dynamics,

modify this equilibrium.

Erosion and

sedimentation cause

vertical movements of

the lithosphere.

Vertical movements of the lithosphere

Mantle

Erosion

Sedimentation

Subsidence

Plastic materialsUplift

Vertical movements of the lithosphere

Horizontal movements of the lithosphere

Plate tectonics nowadays

The engine of the plate tectonics is the subduction itself (not theconvection currents as we thought).

The subducting plate sinks into the mantle, and pulls the wholeplate behind. When it reaches around 670km, the plate stops, because of being less dense than the surrounding materials (as itwas floating). This happens till it suddenly densifies, reachingthese materials lower levels (D’ layer).

This material gets hotter, until it floats and ascends formingmantle plumes. This upwelling of hot rocks heat mantles regionsthat start melting, these regions are called ASTHENOSPHERE.

In opposite regions, divergent plate separete from each other, creating rifts or ridges.

https://www.youtube.com/watch?v=kwfNGatxUJI

Plates tectonic nowadays

http://www.iesalbayzin.org/descargas/AnimacionesBio-Geo/WebCTMA/PlateBoundaries.swf

Bordes destructivos Bordes

Horizontal movements of the lithosphere

Bordes constructivos

CONVERGENT BOUNDARY: Lithosphere is destroyed.Oceanic plate vs. oceanic plate: Island arc. http://www.iesalbayzin.org/descargas/AnimacionesBio-Geo/WebCTMA/SubdOcOc.swfOceanic plate vs. continental plate: Volcanic arc (Orógeno andino o térmico).http://www.iesalbayzin.org/descargas/AnimacionesBio-Geo/WebCTMA/SubdOcCont2.swfContinental plate vs. continental plate: Collisional orogen (Orógeno de colisión, obducción).http://www.iesalbayzin.org/descargas/AnimacionesBio-Geo/WebCTMA/SubdContCont.swf

DIVERGENT BOUNDARY: Plates separation creates new lithosphere, when magma released in ridges, solidifies. Rift valley formation --> mid-ocean ridge (valle rift--> dorsal oceánica).http://www.iesalbayzin.org/descargas/AnimacionesBio-Geo/WebCTMA/RiftValeyAfrica.swf

TRANSFORM BOUNDARY: A transform fault is produced.

HOT SPOT: VOLCANIC ARCHIPIELAGO and INTRAPLATE VULCANISM.

http://www.iesalbayzin.org/descargas/AnimacionesBio-Geo/WebCTMA/PuntosCali.swf

In all cases, plates tectonics is associated to seismic and volcanic phenomena (that can be severe events or not).Both are manifestations of this internal dynamic.

Associated hazards with internal dynamics

Área circumpacífica

Dorsales centroceánicas

Área transasiático-mediterránea

Puntos calientes

Regions of high seismic and volcanic activity.

Associated hazards with internal dynamics

1. Forces from the bending plate.2. Friction between plates.3. Contraction of the plate because of high pressure.

1

2

3

Benioff zone (and hypocentres)

Associated hazards with internal dynamics

http://files.professoralexeinowatzki.webnode.com.br/200000107-c474cc56e8/tectonica_global.jpg