Tectonic geomorphology
RNDr. Petra Štěpančíková, Ph.D.
Institute of Rock Structure and Mechanics
Czech Academy of Sciences, Prague, Czech Republic
Department of Neotectonics and Thermochronology
Outline:
1. Definition of active tectonics, tectonic processes and their types
related to different tectonic regimes
3. Tectonic geomorphology, tectonic control on landscape evolution
4. Response of tectonic processes in fluvial systems, asymmetry of
river basins, related increased erosion and accumulation, river
pattern analysis
2. Landforms characteristic for different types of tectonic movements
(horizontal or vertical)
5. Analyses of fluvial landforms affected by tectonic movements –
river terraces, alluvial fans, analysis of longitudinal river profile and
valley cross sections
6. Mountains uplift and its control on changes in relief, velocity of
geomorphological processes, analysis of mountain fronts
7. Fault scarps, their evolution, erosion, possibilities of their dating
8. Morphometric methods in analysis of landforms controlled by
tectonic processes and assessment of their intensity, planation
surfaces and their different position as an indication of potential tectonic
movements.
9. Paleoseismology, study of prehistoric earthquakes from geological
record, reconstruction of movements
10. Study of paleoseismic parameters of active faults, intensity of
movements, average slip rate, spatio-temporal distribution within the
fault
1. Active tectonics, tectonic processes and their types
resulting from different tectonic regimes
Tectonics – endogenous processes, structures and landforms
associated with Earth´s crust deformation (movements of lithospheric plates)
Lithosphere = solid shell of the Earth (up to 100 km)
Earth´s crust + upper mantle
continental crust (30-80km), density 2.7 g/cm3
Sedimentary, granitic, basaltic layer
oceanic crust (5-10km), density 2.9 g/cm3
Sedimentary, basaltic layer
direct observations – drills, geologic information (xenolites)
Mohorovičič discontinuity –
crust/mantle – density change, higher
velocity P-waves
Lithosphere / asthenosphere
(semifluid) 3.6 g/cm3, lower viscosity
– below lithospheric plates
– velocity of seismic waves
Global scale tectonics: origin of continents and ocean basins
Plate tectonics
107 m
10,000 km
Scale 1:100,000,000
106 m
1000 km
Scale 1:10,000,000
Regional Neotectonics
Satellite images
Global Neotectonics
mountain chainsmicroplates
105 m
100 km
Scale 1:1.000,000 104 m
10 km
Scale 1:100,000
103 m
1 km
Scale 1:10,000
Local scale: individual landforms such as folds,
fault scarps etc.
satellite images
Active Tectonics
Tectonic Geomorphology
10-1 m
10 cm
Scale 1:1
100 m
1 m
Scale 1:10
101 m
10 m
Scale 1:100
Structural Geology
Petrology
outcrop/ hand sample
offset channels
tectonic breccia
Time scales of tectonics:
depend on spatial scale at which the processes act:
Development of continents - thousands of millions years
Large ocean basins - hundreds of millions years
Small mountain ranges - several millions years
Small folds to produce hills - several hundred thousands years
Fault scarps - suddenly
during earthquake
Neotectonics - crustal movements starting after the youngest
orogenic phase or related to the youngest stress field occurring in
the late Neogene and Quaternary
Active tectonics – tectonic processes that caused deformation of
the Earth´s crust of local scale and on a time scale
significant for humans (EQs)
Active faults – moved during last 10.000 yrs – Holocene
(paleoseismology)
Potentially active faults (capable faults) – moved during Quaternary
(2.6 million yrs)
Rates of tectonic processes:
Very variable – 0.00X-X mm/year for fault displacement
X cm/year for movement on plate boundaries
Tectonic processes - driven by
forces in the depth that deform
the crust => origin of ocean
basins, continents, mountains
Litosphere broken into plates - relatively move; triple junction
divergent – extension (spreading), convergent – shortening (subduction) video!
Tectonic cycle
Video!
Video!
Active Tectonics: confirmation of plate tectonics…
• Earthquakes
• Volcanoes
• Faults
World Seismicity, 1963–2000
Video!
• Topography
• Surface
deformation
Producing new lithosphere in ocean ridges, subduction of old one and
plates sliding along each other – produce stress (force per unit area) and
strain (deformation – change in length, volume).
Seismic tectonic movements
When the stress exceeds the strength of rocks, then rocks fail (rupture),
energy is released in a form of an earthquake (seismic waves) and
faulting (breaking the rocks, rock deformation).
Video!
location
P-waves followed
by S-waves
After the EQ, stress is accumulated again.
Earthquake cycle (seismic cycle):
1. accumulation of stress = produces elastic
strain (not permanent)
2. during earthquake stress is released when
rocks break and permanent displacement
occurs, then strain also drops = elastic
rebound (deformed material in original shape)
Video!
Magnitude vs Intensity
Richter´s magnitude
logarithmic scale obtained by
calculating the logarithm of the
amplitude of waves
M = log a
Moment magnitude Mw
energy is transformed in
• cracks and deformation in rocks
• heat,
• radiated seismic energy Es.
The seismic moment M0 is a measure
of the total amount of energy that is
transformed during an earthquake.
Rossi – Forei – X grades (1883)
XXII
MCS – Mercalli – Cancani - Sieberg (1902)
MSK -64 – Medvedev-
Sponheuer-Kárník
MMI – Modified Mercalli (in USA)
EMS-98 - European Macroseismic Scale
I. Nepocítěno Zemětřesení nebylo pocítěno.
II. Stěží pocítěno Pocítěno jen velmi málo jednotlivci v klidu v domech.
III. Slabé Pocítěno uvnitř budov některými osobami. Lidé v klidu pociťují jako houpání nebo lehké chvění.
IV. Značně pozorované
Zemětřesení uvnitř budov cítí mnozí, venku jen výjimečně. Někteří lidé jsou probuzeni. Okna, dveře a
nádobí drnčí.
V. Silné
Uvnitř budov cítí většina, venku někteří. Mnozí spící se probudí. Někteří jsou vystrašení. Budovy vibrují.
Visící objekty se značně houpají. Malé předměty se posouvají. Dveře a okna se otvírají a zavírají.
VI. Mírně ničivé
Mnozí lidé jsou vystrašeni a vybíhají ven. Některé předměty padají. Mnohé budovy utrpí malé
nestrukturální škody jako např. vlásečnicové trhliny nebo odpadnuté malé kousky omítky.
VII. Ničivé
Většina lidí je vystrašena a vybíhá ven. Nábytek se posouvá. Předměty padají z polic ve velkém
množství. Mnohé dobře postavené běžné budovy utrpí střední škody: malé trhliny ve zdech, opadá
omítka, padají části komínů; ve stěnách starších budov jsou velké trhliny a příčky jsou zřícené.
VIII. Těžce ničivé
Mnozí lidé mají problémy udržet rovnováhu. Mnohé domy mají velké trhliny ve stěnách. Některé dobře
postavené běžné budovy mají vážně poškozené stěny. Slabé starší struktury se mohou zřítit.
IX. Destruktivní
Všeobecná panika. Mnoho slabých staveb se řítí. I dobře postavené běžné budovy utrpí velmi těžké
škody: těžké poškození stěn a částečně i strukturální škody.
X. Velmi destruktivní Mnohé dobře postavené běžné budovy se řítí.
XI. Devastující Většina dobře postavených běžných budov se řítí. I některé seismicky odolné budovy jsou zničeny.
XII. Úplně devastující Téměř všechny budovy jsou zničeny.
Macroseismic effects on the surface
- crucial factors
• Size of earthquake, depth of hypocentre (focus), distance from the
epicentre, response of surficial layers
• Distance of faults, orientation of faults in epicentral area
• Locally – lithology and physical state of the rocks
Depth of groundwater level
Geology
Higher amplitudes – worse effects
Mexico city 1985, M = 8, epicentre 350km far away, 10,000 casualties
Distance from the epicentre
- wave type
P, S waves – high frequency
Surface waves – low
frequency
Low buildings – high proper
frequency
High buildings, skyscrapers –
low proper frequency
Acceleration of bedrock (ground motion)
Horizontal component
Vertical component (amplitudes over 50% lower than horizontal)
Relation – magnitude and intensity
Effects of earthquakes
Primary effects: ground-shaking motion and rupture of the surface
(shear or collapse of large buildings, bridges, dams, tunnels, pipelines)
Chi-chi EQ Taiwan 1999 with M=7.6 Landers EQ, Emerson fault, CA 1992, M=7.3
Secondary effects:
Short-term
Liquefaction – water-saturated material transforms to liquid state (loose soil
into mud) during shaking, compaction causes an increase of pore-water
pressure = material loses shear strength and flows.
Water under the soil rises and the ground sinks causing extensive damage to
buildings, roads and other structures.
Buildings tilted due to
soil liquefaction, 1964
earthquake, Japan.
Landslides
Seismic Seawaves – Tsunami
Fires
Floods – following collapse of dams
Long-term
Regional subsidence
Change in groundwater level
Costarica, 2009, Mw=6.2,
180 landslides
Tectonic creep – aseismic movements
Displacement along a fault zone accompanied by minimal earthquakes, more
or less continuous, narrow zone
Geodetically detectable (GPS, SLR, etc.... )
Less damage from creep – generally along narrow fault zones subject to slow,
not much studied in – no seismic hazard
Creep rate measured by creepmeter installed across the fault – typically 5 mm/year,
max in Fremont 7.8-8.5 mm/year
Hayward fault – SAF zone, San Francisco
Bay area
Between 5 and 12 km in depth is
believed to slip entirely in earthquakes,
but the surface and deepest part of the
fault also slips by a process of aseismic
creep.
Creep since 1896 large EQ, the creep
partially releases the strain energy on
the fault
High rate: slow damage of roads, sidewalks, building etc.
Berkeley – Memorial stadium
3.2 cm in 11 years,
periodic repairs needed
Berkeley, offset sidewalk
Contra Costa,
deformed road
Hayward, offset fence
Higher creep rate:
Calaveras fault (SAF zone)
Creep rate – varies
1910-1929 no creep, based on offset in two sidewalks constructed in 1910 and
1929, and pipeline laid in 1929
1929 ......- creep commenced, with 8 mm/yr (average)
1961 - 1967, slip rate about 15 mm/yr
1979....2 sites monitored in Hollister with 6.6 mm/yr and 12 mm/yr (2.3km NW)
20.000 earthquakes a year - small, strain not
accumulated and released by slow creep – not able to
produce a large EQ
Hollister, twisted house
Calaveras fault - vinařství
Creepující strom
2. Tectonic geomorphology, role of tectonics
in relief formation
Landforms – surficial features which make up the landscape
All scales – mountains, alluvial fans, hills, canyons, slopes etc.
Geomorphology – study of nature, origin, and evolution of landscape
A) Geological factors – important, landform development is related to
underlying structure of the Earth
Structure – includes rock and soil type, nature and abundance of fractures,
faults, folds
B) Geomorphic processes - weathering (physical, chemical), fluvial
erosion/deposition, glacial, eolian (wind), mass wasting (slope failure),
tectonic, and volcanic
C) Natural variables - geology, climate, vegetation, base-level, human
inteference - influence the type and rate of the processes
Tectonic geomorphology – study of landforms produced by tectonic
processes; study how tectonics controls erosion, deposition, landforms;
from morphology we can infer fault kinematics
Geomorphology – valuable tool in active tectonic studies because the
young tectonic processes are reflected in morphology and Quaternary
deposits present on a site
e.g. study of stream channels and related deposits offset by faulting –
may reveal amount of displacement, timing of the last few earthquakes at
the site – critical for seismic hazard evaluation
Process-response models
-qualitative and quantitative representations how processes influence
landform development
-e.g. alluvial fans – result from tectonic, fluvial processes or/and changes in
climate conditions (various causes)
We should understand all the processes to be able to distinguish between
them (Spain vs Bohemian massif – fluvial terraces, alluvial fans)
Uplift
Vertical movements produce the large landforms on the Earth surface – uplift
Bedrock uplift – influenced by both tectonic and geomorphic processes
Different theories on interaction between tectonics and landscape developed
Not only pure uplift - combination of vertical + horizontal movements so there
are not black-and-white definitions
- geomorphic processes: erosion, denudation, deposition, weathering
Uplift – isostatic uplift + tectonic uplift = bedrock uplift
Isostatic uplift
Rainfall can never melt enough ice to
lower the surface of an iceberg to the
water line. This is because ice melted
above the waterline is largely
replaced by “uplift” of submerged ice.
Isostatic uplift – ice has 90% of
density of seawater
If 10 tons is melted from the
exposed surface of an iceberg, it is
compensated by 9 tons of ice
raised by isostatic uplift – isostatic
rebound
= pure uplift (no shear, no
tensional failure of ice)
Isostasy in mountains
Continental crust (density of about 2,700 kg/m3) „floats“ on mantle with a
density of about 3,300 kg/m3 – a density contrast of roughly 82% (90%
contrast for oceanic crust with a density of 3,000 kg/m3) – analogy with ice
Fluvial and glacial denudation of 1,000 m only seems to significantly lower a
mountain range because it is largely compensated by 820 m of concurrent
isostatic rebound.
Video!
Fluvial and glacial erosion – isostatic uplift caused mainly in valley floors (video)
Mass removal (denudation) – pure isostatic uplift in all parts of the landscape
Larger space and longer time - for pure uplift, tectonic denudation, or burial
Smaller forms and shorter time - for tectonic displacements and geomorphic
processes
Tectonic uplift
- driven by tectonic processes, mountain-building processes – convergent plate
boundaries
Tectonic mountain-building forces may stop but the resulting isostatic
adjustments will continue as long as streams transfer mass from mountains to
sea.
Tectonic geomorpholgy of mountains, Bull 2007
Bedrock uplift = Tectonic uplift + Isostatic uplift
Tectonic uplift – induce higher erosion,
Higher altitude – different processes, different climate - influence isostatical uplift
Climatic changes are dominant because they quickly affect geomorphic
processes throughout a drainage basin – precipitation, discharge
X uplift on a fault zone is local and the resulting increase in relief
progresses upstream relatively slowly
Surface uplift = change of altitude influence geomorphological processes
The surface rupture of the 1999 Ch-Chi formed a waterfall (8 m
high). River erosion tries to erase this step (several m retreat)
Tectonic uplift induced incision