A new geodetic datum for Nepal after the 2015 Gorka Earthquake · Gorka earthquake and May...
Transcript of A new geodetic datum for Nepal after the 2015 Gorka Earthquake · Gorka earthquake and May...
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A new geodetic datum for Nepal
after the 2015 Gorka Earthquake
Chris Pearson
Niraj Manandhar
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Required by GPS
No deformation model
Datums and epoch dates change frequently
Approximate transformationNo NDMITRF
Nepal Everest
Inexact No deformation model
Satellite Laser Ranging
Very Long Baseline Interferometry
DORIS: DopplerGNSS (GPS)
ITRF Measurement Techniques
Nepal Everest datum has no mechanism to correct for crustal deformation
No epoch date
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Required by GPS
No deformation model
Datums and epoch dates change frequently
NDMITRF2014
Modernized datum for Nepal
Stable coords deformation model
Satellite Laser Ranging
Very Long Baseline Interferometry
DORIS: DopplerGNSS (GPS)
ITRF Measurement Techniques
Modernized geodetic datum aligned with ITRF2014Coordinates transformed to 1 Jan 2016 using the a
national deformation model
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Positio
n
How the NDM works
Time2005
NDM
Patch
2016
Modernized datum coordinate
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Secular velocity field
• Velocity from four recent studies were aligned with the ITRF2014
velocities
• The combined velocity field was used to produce a grid file with a
density of 20 points/degree
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Residuals from alignment
0
5
10
15
20
25
30
35
-3 -2 -1 0 1 2 3
Freq
uen
cy
North Residuals mm/yr
w-o allignment
0
10
20
30
40
50
60
-3 -2 -1 0 1 2 3
Freq
uen
cy
East Residuals mm/yr
w-o allignment
0
20
40
60
80
-3 -2 -1 0 1 2 3
Freq
uen
cy
East Residuals mm/yr
after allignment
0
10
20
30
40
50
60
-3 -2 -1 0 1 2 3
Freq
uen
cy
North Residuals mm/yr
after allignment
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Secular velocity field
• Velocity from four recent studies were aligned with the ITRF2014
velocities
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Verification of earthquake models
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Two possible models for Gorka Earthquake
Galetzka et al. 2015 (JPL) Wang et al in prep (SOPAC)
RMS Galetzka
E m 0.21
N m 0.11
U m 0.08
RMS Wang
E m 0.07
N m 0.02
U m 0.03
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Post seismic relexation
Mencin et al Nature Geosciences 2016
43/1 itt
ikikkk ettHPttHEtvtm
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Control
• The stations of the CALTECH network now operated by UNAVCO
can be adopted as a 0 order network of CORS
• Coordinates determined using specialist GNSS software to give
coordinates precisely aligned to the ITRF at epoch 2016.0
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Deformation models in survey adjustments Example: Patch for an Earthquake
Measured Vector
Measured Position and Vector
Ground Displacement
Corrected Nepal2016 vector EPOCH 2016.0
National Deformation Model
Patch
Earthquake
Epoch 2016.0
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Adjustment of GPS before and after the Gorkha Earthquake
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First Order adjustment Preliminary
results• Data from 2009-2016
• 222 baselines 217 used 5 rejections
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Results from adjustmentmax min mean +- 1 sig RMS
m m m m m
Combined pre & post free adjustment seuw= 1.03
E 0.11 -0.12 -0.001 0.002 0.022N 0.15 -0.29 0.000 0.002 0.027U 0.34 -0.39 -0.003 0.005 0.069
Combined pre & post constrained adjustment Seuw=1.2
E 0.09 -0.12 -0.002 0.002 0.023
N 0.15 -0.29 -0.001 0.002 0.027
U 0.32 -0.38 -0.005 0.005 0.074
Combined pre & post constrained wo NDM Seuw=26.7
E 0.30 -0.49 0.000 0.008 0.104
N 0.92 -1.73 -0.022 0.028 0.383
U 1.19 -0.85 0.005 0.022 0.295
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Significant baselines without aftershock model
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Distortion grid Nepal 2016.0 -Nepal-Everest transformation
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Conclusions
• datum aligned to a realization of the ITRF
• common reference epoch after the recent
sequence of earthquakes
• deformation model
• Velocity model
• Earthquake displacements
• Control
• Top level control CORS network
• Establish lower order control relative to the CORS
– New marks surveyed with GPS
– Readjust existing measurements starting with 1st order
• correction grids to transform GIS coordinates
from Nepal Everest into the new system.
DO
NE
to d
o o
r underw
ay
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Combined vertical displacements from Gorka earthquake and May aftershock