N S Looking Inside the Continents from Space: Insights into Earthquake Hazard and Crustal...
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Transcript of N S Looking Inside the Continents from Space: Insights into Earthquake Hazard and Crustal...
NS
Looking Inside the Continents from Space: Insights into Earthquake Hazard and
Crustal Deformation
NS
IndiaTibetan Plateau5 cm/yr
Earthquake Hazard in the Alpine-Himalayan Belt
Alpine-Himalayan Belt
75% of earthquakes killing more than 10k since 1900.
Mapping Surface Deformation (Strain)
• Although they can not be predicted, earthquakes are preceded by the slow build up of tectonic strain.
• Repeated satellite radar measurement can be combined to measure surface displacements at the mm level over large areas.
• The team have pioneered methods for mapping deformation using satellite radar.
• A radical increase in radar data quality and quantity from the Sentinel-1 mission will allow strain to be mapped with high accuracy over large regions for the first time.
Wright, Parsons & Fielding, GRL 2001
0
6
-6
mm/yr
North Anatolian Fault, 23 mm/yr
Objectives
A: Make fundamental advance in the mapping of tectonic deformation (for
Alpine-Himalayan Belt and East African Rift)
B: Improve seismic hazard
assessment
C: Understand how the continents deform
in space and time
Basic Question 1: What is the Mechanical Structure of Fault Zones Controlling the Earthquake Cycle
~20 mm/yr
Postseismic, 1997 Manyi EarthquakeRyder, Parsons, Wright & Funning, GJI, 2007
LOS
disp
lace
men
t (cm
)Poro-elasticity
Visco-elastic relaxation
Afterslip
0
4
-4
cm
Earthquakes with Mw ≥ 6.7. Black: 1991-2012 (InSAR era); Red: 1978-1991
Poro-elasticity
Visco-elastic relaxation
Afterslip
• Modelling the earthquake cycle has been hampered by the lack of observations (relatively few events where data available + short time periods compared to length of cycle)
• We will build and test dynamical models of the earthquake cycle, constrained by observations of different parts of faults at different stages in the cycle
Basic Question 1: What is the Mechanical Structure of Fault Zones Controlling the Earthquake Cycle
x
y
Red = weak lower crustBlack = strong lower crust
Horizontal
VerticalBasic Question 2: What is the Mechanical Structure of
Continental Lithosphere?
Copley, 2008
a
ba b
Accuracy Requirements and Earthquake Hazard
• 96% of all earthquake deaths are in regions with strain rates greater than 1mm/yr over 100 km (10-8/yr)
• 77% of fatalities occur where deformation rates are ≤ 5 mm/yr over 100 km.
Cum
ulati
ve p
erce
ntag
e of
ear
thqu
ake
deat
hs
Magnitude of tectonic strain (x10-9 /yr)
Sentinel-1 makes this possible
Envisat Sentinel-1
Stand-alone mission not specifically designed for InSAR
20 year operational program, designed for InSAR
Haphazard acquisition strategy (multiple modes)
Systematic acquisitions over deformation belts
Archive typically has ~30 images over 7 years
12 day revisit → 30 images per satellite per year
Loss of signal due to long time gaps or large orbital separations
6 day revisit (with two satellites), small orbital separation
Achieving 1 mm/yr accuracy
Wang, Wright et al, 2008
Accurate Orbital Models
Atmospheric Corrections
0
5
-5
mm/yr
Achieving 1 mm/yr accuracy
Wang, Wright et al, 2008
Error for mission with 12-day repeat
Duration of time series (years)
Leng
th s
cale
of o
bser
vatio
n (k
m)
0
5
-5
mm/yr
Wang & Wright, GRL 2012
Producing High-resolution Velocity and Strain Fields from InSAR and GPS
East Velocity Strain
17/11/12
SRTM Digital elevation data
N
10 km
Lepsy fault
Single event? Length 100 km, slip 10 m .....Magnitude 8.0
10 m
Richard Walker, pers comm
++
++
+ +
Identifying previously unknown faults with high-resolution imagery and DEMs
Lepsy fault, Kazakhstan (Walker, Jackson et al, in preparation)
The TeamW
right
Tectonic DeformationA1: InSAR Time Series [Leeds: Wright, Hooper, PDRA #1]A2: Atmospheric Errors [Glasgow: Li, PDRA #2; Reading: Wadge]A3: Orbital Errors [UCL: Ziebart, PDRA #3]Seismic HazardB4: Strain/Hazard Mapping [Leeds: Wright, Walters (COMET+ PDRA #4)]B5: Finding Faults [Oxford: Walker, PDRA #5; Cambridge: Jackson]B6: Time-dependent Hazard [Oxford: England, Elliott (COMET+ PDRA #6), Parsons]ModellingC7: Earthquake Cycle Models [Oxford: Parsons, PDRA #7; Leeds: Houseman, Wright]C8: 3D Numerical Modelling [Cambridge: Copley; Leeds: Houseman; Oxford: England]C9: East African Rift [Bristol: Biggs; Reading: Wadge]
Pars
ons
Plus 5 PhD students, Partner Nocquet (GPS)
Impact Partners
Why us? Why now? Ambitious, Frontier Science
Velocity and strain fields and resultant models will transform our understanding of continental deformation.
Timely Exploits radical increase in SAR data from the Sentinel-1
mission, an opportunity for leadership in this field.
Achievable Builds on more than a decade of development by the
investigators.
Societal Impact Accurate knowledge of the distribution of seismic hazard is
the first step in hazard mitigation.
High-resolution deformation
measurements from Sentinel-1
Earthquake Hazard
Earthquake source models
Precise Orbits for Sentinel-1
Water Vapour measurements
Earthquake Cycle Deformation Models
Regional Strain Maps
Fault Map for Alpine-
Himalayan Belt
3D Models of Continental Tectonics
What this project will deliverData
Derived products
Models
Information
Q. Management
Q. What will the students do?Student #1: Copley, Jackson (Cambridge)Constraining the structure and rheology of the lithosphere(Using satellite gravity and seismic structure to investigate thermal and rheological structure of the lithosphere)Student #2: Jackson, Copley (Cambridge), Elliott (Oxford)Active faulting and rift evolution in East Africa(Analysing DEMs and Optical imagery to investigate faulting in EAR. Linking this to variations in lithospheric thickness and mantle structure, and to mechanisms of recent seismic activity derived from InSAR/seismology)Student #3: Houseman, Wright (Leeds)Mechanisms of strain localisation in the Crust(Developing 2D and 3D FEMs that include anisotropic viscoelastic constitutive relationships,due to CPO, and feedback mechanisms) Student #4: Hooper (Leeds), Biggs (Bristol)Automatic detection of volcanic unrest(Applying techniques developed in the proposal to volcanic deformation on a large scale) Student #5: Biggs (Bristol), Wadge (Reading)Active volcanism and magma intrusion in East Africa(testing whether ratio of extrusion/intrusion in the crust is a function of degree of crustal extension)
Technical challenges:• Solar and Earth radiation photon pressure modelling• Atmospheric drag• Antenna thrust (recoil forces from signal transmission)• GPS phase centre determination/multipath modelling• Orbit product validation (laser ranging residual analysis, repeatability)
True trajectoryBiased orbit (mismodelled dynamics)
5cm error
JPL/UCL orbit (1cm accuracy)
Jason-1
Sentinel-1
Q. Can we be confident of
achieving 1cm orbital precision?
Q. How well can we remove atmospheric noise?
Jolivet et al., 2011
We assume, conservatively, that weather models will correct 50% of single interferograms
Q. Can we really estimate water vapour in near-real time?
For N=15, error in path delay ~ 2 mm; For N=100 (~3 years), error ~1 mm
Q. Will it be coherent at C-band?
C-band coherence (1 year = red; 1 cycle = red+orange)L-band should be coherence in most places over 13 days
Wright et al., Fringe 2011
Q. Why East Africa?C
raig
, Ja
ckso
n et
al.,
201
1
Lithospheric thickness
Ham
mon
d et
al.,
201
3
Shear-wave anomaly (75 km)
Q. How much better than existing missions?
Envisat Data, 70 Day Repeat, 7 years data
Sentinel-1A Data, 12 Day Repeat, 3 years data
40% of areas straining above
10-8 yr-1
80% of areas straining above 10-8 yr-1 [90 %
with two satellites]
Wright et al., Fringe 2011
Q. How to turn strain into hazard maps?
Number of earthquakes forecast with M > 5.66, from Bird et al., 2010. Green = 1 earthquake per century in a 100 x 100 km area .[Crude because strain data is low resolution]
Q. Time dependent Hazard?
3 September 2010: Darfield, M7.1
21 February 2011: Christchurch, M6.3
New Zealand Earthquakes 2010-11