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The Earth Physics Institute of Paris
is a higher education and research establishment.
The research institute is represented by: 14 teams
and 3 observatories, and is associated with the CNRS.
Tectonics aims to study lithosperic deformation.
The lithosphere is the Earth's upper layer.
This is the outermost layer, which is about 100 to 150km long.
It's length is divided into different distinct plates.
We can see them on this map.
Seismicity, illustrated by these focal mechanisms,
allows us to see plates boundaries and deformations.
Since the work of Wegener in 1912,
when he discovered that Africa and South America fit together,
we realized that there had been huge surface displacements in the history of the Earth.
It had remained an exceptional discovery up to the 1950s and 1960s
when plate tectonics studies truly took off.
The Americans and the English discovered
magnetic anomalies in the oceans,
the distribution of earthquakes in the middle of the oceans,
along the lines od plates, and in the subduction zones.
Let's take for example the San Andreas Fault.
The blocks, limited by these faults,
move in relation to each other, permanently
and continuously 1 centimeter per year.
Plate tectonics is the biggest discovery
of the 20th century for earth sciences.
It provides an intellectual framework
in which to understand what is happening on the Earth's surface,
especially on the continents.
We observe deformations, mountain chains, and rift valleys.
Nowadays, we have a good comprehension of geological phenomena
in terms of plate tectonics.
Our observations are made firstly in the field.
It's the most important thing.
We analyze structures
at an outcrop scale, for regions or continents.
What kind of rock we can find there, what form and what composition.
These phenomena on the surface are important
to figure out what is happening in the deep.
It's important to see what a zone looks like
geographically and morphologically.
We complete with observations on a large scale
thanks to space technology.
We are big consumers of space imagery
particularly in the visible.
We had Lansat satellites in the 70's,
Spot satellites in the 80's and 90's,
and nowadays, we utilize very-high resolution satellites
with one meter ground pixels accuracy.
We use radar interferometry as well.
This technology is more recent, dating to the beginning of the 90's.
It allows us to measure ground deformation precisely
following an earthquake or prior to a volcanic eruption.
Thus, we use field and satellite observations.
The study of the deformation of continents
requires us to bring back samples
in order to analyze their mineralogical composition,
and to determine the age or time they deformed.
The time factor is a crucial element.
The numerical modeling
enables us to replicate real field situations in
the laboratory setting,
and therefore understand how a region deforms itself.
How fast does this happen? And by what mechanism?
The topics we're concerned about in the continental deformation,
are the actual deformations linked to faults,
earthquakes,
within larger time and space scales.
How the evolution of the continents surface
allows us to understand what's happening in deep.
Then, we have a modeling processes approach
which deals with the deformation of the continents,
numerical, for now,
which was based on analogical experiences in the past.
These experiences are responsible for the reputation of this laboratory.
I'm interested in the deformations of the lithosphere
through various time scales, from earthquakes,
active faults, that range over a couple of years
to hundreds of years,
to the evolution of deformations
over several million year periods.
The faults absorb the deformation of a continent.
On the surface, this generates earthquakes.
In depth, rocks have been deforming continuously.
You have different type of faults
in the crust and the lithosphere
which cause deformation mechanisms.
Reverse faults lead to a shortening.
Using different scales, we observe
a portion which goes up over the other.
Normal faults cause extension,
with this kind of movement,
and strike-slip faults cause blocks to slip.
These fault zones are located all around the Earth.
These reverse faults produce mountain chains
such as the Himalayas, or the Alps, for example.
We can find normal faults under circumstances like extension.
For example: mid-oceanic ridges
or zones where an ocean start to split open.
For example, in the Afar region, in Ethiopia,
you can find strike slip faults in various situations.
Some are huge, either in consideration of the limit of the plate tectonics,
like the San Andreas fault,
or in collision zones, as is the case for the one located between India and Asia.
All these deformation mechanisms, at continental level,
are different and can combine to absorb
what the plate tectonics impose.
What is important in the study of the deformation of the continents,
is the contribution of the surface morphology to the continental crust.
What does a landscape look like?
What can it tell us about the deformation of the continents?
What is the connection between deep phenomena inside the crust,
or deeper in the lithosphere and the surface,
and what does it mean in terms of interactions
with the climate?
On a map of the Asian continent,
we may observe some regions at low altitude
such as Western Siberia, East of the Urals.
Some regions are higher:
the Tibetan Plateau, the Himalayas, the Tien Shan mountain range...
These various altitudes experience deformations.
We try to understand what kind of deformations
lead to the formation of such a plain, or mountain,
or this long valley...
Tectonics create the topography of the land.
It is block movements in relation to each other,
that affect the surface of the Earth,
on the crust, the lithosphere,
on the first 30 or 100 km of the surface.
Here, India enters into Asia.
You have to compress all these rocks.
It causes them to rise and this creates elevations of land.
There are external factors
such as erosion which also sculpts landscapes.
One of my projects begins on the Kunlun mountains,
here, on the northwest border of the Tibetan plateau,
at the south portion of the Tarim basin.
Here is a nice tectonic object,
with a closed basin called "endoreic"
which preserves all the sediments from the mountains nearby
and also serves to stock everything around.
It's necessary to look for geological information
in the basin and the mountain range in an attempt to understand
how tectonics, erosion and climate interact.
These things are currently discussed according to models.
Erosion unloads sediments,
thereby modifying forces.
When the sediments are dropped off in a basin,
it creates sediment loads, changing the forces.
How does erosion and sedimentation
modify tectonics?
These things are studied according to models
and we possess limited geological information regarding this.
We wish to constrain the evolution of these systems.
Is there an evolution from one to another?
Does the mountain range evolve during climate change?
When is there more or less erosion?
Paleo-seismology aims to create catalogues of earthquakes
over time, for a precise location.
We seek to determine the frequency of earthquakes on a specific fault line.
It's important for the construction of buildings
in terms of the seismic risk.
First, we locate the fault.
Over time, geological layers
from centimeter to meter, settle flat
in the lake bottom or the lower portion of a plain.
Every time there's an earthquake, layers are disturbed
and staggered horizontally or vertically.
Then, time replaces non-disturbed layers.
When we cut a section through these layers,
the disturbance is visible.
If we are able to date these layers with carbon-14,
we can date the earthquake, in a certain location.
The Levant fault is a propitious place for this kind of study.
Here we obtained the measures of 14 successive earthquakes over time,
and we can give an age range.
For the Levant fault,
the earthquakes come back every 1000 years.
This is important because on this part of the fault,
the last significant earthquake dates from 1202.
We're looking for the logical course of the arrangement of the earthquakes.
We want to know how earthquakes
divide laterally along a 1000km fault,
and whether earthquakes have a logic, spread to one side and then to another
or, if on the contrary, occur side to side at random.
To understand the active faults
and determine how they evolve throughout time
there is a field of study growing nowadays
about the impact of the geometry of the concerned structures,
to see how a fault is going to evolve over time,
the repercussions on the control of the deformation
and the progress of an earthquake.
You have to link the study of the earthquake of yesterday
to past earthquakes.
IPGP collaborated with South Africa recently.
We want to understand the altitude of the southern zone of Africa.
Why is this region located higher,
while there is no orogenic activity on the surface?
Where does this altitude come from?
Other regions are still not well known.
Particularly the fringes of the Arctic Ocean,
northern Canada or northern Siberia.
In tectonics, we work on different concepts:
strike slip faults, mountain chains, and rifts.
They are always connected with a specific geographic object.
We work on a particular mountain range
because it tells us what's happening in this region
but also in mountain ranges all around the world.
Therein resides a dual goal:
to comprehend the continental lithosphere
in a specific geodynamic context,
while also seeking to understand a specific region.
Subtitled by MFP.