new zealand’s long term tide gauge record€¦ · rising global sea levels source: church &...
TRANSCRIPT
New Zealand’s Long Term Tide Gauge Record
and the effect of
Seismically Induced Vertical Land Motion
Paul Denys1, John Beavan2, John Hannah1, Neville Palmer2,
Mike Denham1, Chris Pearson1 and Sigrum Hreinsdottir2
1 School of Surveying, Otago University, Dunedin 2 GNS Science, Lower Hutt
Presented at th
e FIG W
orking Week 2017,
May 29 - June 2, 2
017 in Helsinki, F
inland
The IPCC Assessment
Source: IPCC (2013)
Snow cover
Ice extent
Ocean heat content
Sea level change
Rising global sea levels
Source: Church & White (2011)
Globally distributed tide gauge data
Average since 1880 : +1.7 ± 0.3mm/yr
GSL has risen ~20cm during the C20th
Global Network of Tide Gauges
Tide gauge measurement system
Source: sealevel.colorado.edu/content/tide-gauge-sea-level
The global network of tide gauges is a poorly distributed sea level
measurement system
But, it offers the only source of historical, precise, long-term sea
level data
Tide gauge stability
Source: sealevel.colorado.edu/content/tide-gauge-sea-level
Levelling : local stability of the tide gauge structure
cGPS : regional stability
Source: sealevel.colorado.edu/content/tide-gauge-sea-level subsidence
uplift
subsidence
uplift
Lyttelton – Local stability levelling network
Reference Marks
GPS TGBM
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
0
5
10
15
20
25
30
35
40
45
50
55
B418
Year
Ben
ch
ma
rk T
ren
d (
mm
)
DHAM
BF1U
B40V
DJMF
DHAR
DHAT
DHAQ
DHAP
DHAN
+0.3 mm/yr
1900 1920 1940 1960 1980 2000 2020
0
500
1000
1500
2000
2500
3000
Dunedin
Vel: +1.3 +-0.1mm/yr rms: +-34mm
Year
TG
Tre
nd
(m
m)
RSL Trends - NZ
Lyttelton
Vel: +1.9 +-0.1mm/yr rms: +-30mm
Wellington
Vel: +2.2 +-0.1mm/yr rms: +-37mm
New Plymouth
Vel: +1.3 +-0.4mm/yr rms: +-57mm
Auckland
Vel: +1.6 +-0.1mm/yr rms: +-34mm
Relative sea level trends - NZ
Average: +1.7 mm/yr
Port environments - challenging
• GPS/GNSS often established in poor environments
– High rise building
– Topography e.g. volcanic crater
– Reclaimed land compaction
– Wharf stability e.g. wooden
– Port operations
– Port construction
• Conflicting requirements
– Unobstructed sky visibility and stability/bedrock
Auckland CDB
Port Lyttelton
GP
S h
eig
ht
tim
e se
ries
1996 1998 2000 2002 2004 2006 2008 2010 2012 2014
0
50
100
150
200
250
300
DUND
Heig
ht
Tre
nd
[m
m]
Time [years]
DUNT
OUS2
OUSD
MQZG
LYTT
AVLN
WGTT
WARK
WGTN
TAKL
AUCK
Auckland
-0.6 mm/yr
Wellington
-3.0 mm/yr
Lyttelton
-0.5 mm/yr
-1.4 mm/yr
Dunedin
-1.0 mm/yr
Auckland : cGPS replaced
TAKL: vH = -0.54 mm/yr AUKT: vH = -0.63 mm/yr
TAKL + AUKT: vH = -0.62 mm/yr
2002 2004 2006 2008 2010 2012 2014
-40
-30
-20
-10
0
10
20
30
Heig
ht
(mm
)
Years
Wellington Height connection TG - cGPS
Wellington – Height connection TG – cGPS
2000 2002 2004 2006 2008 2010 2012 2014 201627.786
27.788
27.79
27.792
27.794
27.796
27.798
27.8
27.802
27.804
27.806
rms = ±1.15 mm relative to a -0.98 mm/yr linear fit
1 mm
Year
Heig
ht
Dif
fere
nc
e (
metr
es)
cGPS -3 mm/yr
Hgt Diff +1 mm/yr
TG -2 mm/yr
Wellington – Vertical trend
2000 2005 2010 2015
-80
-60
-40
-20
0
20
Heig
ht
(mm
)
Years
1998 2000 2002 2004 2006 2008 2010 2012 2014
-80
-60
-40
-20
0
20
Heig
ht
(mm
)
Years
WGTN
vH= -2.9 mm/yr
WGTT
vH= -3.1 mm/yr
Wellington – Slow Slip Events
2000 2005 2010 2015
-60
-40
-20
0
20
Heig
ht
(mm
)
Years
1998 2000 2002 2004 2006 2008 2010 2012 2014
-60
-40
-20
0
20
Heig
ht
(mm
)
Years
WGTN
+16.5 mm
WGTT
+13 mm
Kapiti Coast slow slip events
cGPS -3 mm/yr
Hgt Diff +1 mm/yr
SSE +1 mm/yr
TG -1 mm/yr
Lyttelton – Christchurch earthquake events
LYTT
vH= -0.5 mm/yr
MQZG
vH= -1.6 mm/yr
2000 2005 2010 2015
0
50
100
Heig
ht
(mm
)
Years
2000 2005 2010 2015
-40
-20
0
20
Heig
ht
(mm
)
Years
Lyttelton – Post-seismic decay
LYTT
vH= -0.5 mm/yr
MQZG
vH= -1.6 mm/yr
2000 2005 2010 2015
-40
-20
0
20
Heig
ht
(mm
)
Years
2000 2005 2010 2015
-30
-20
-10
0
10
20
30
Heig
ht
(mm
)
Years
2000 2005 2010 2015
-40
-20
0
20
Heig
ht
(mm
)
Years
Dunedin – Far-field earthquake events
1996 1998 2000 2002 2004 2006 2008 2010 2012 2014
-40
-20
0
20
Heig
ht
(mm
)
Years
Dusky Sound 2009 Macquaire Island 2004
Secretary Island 2003
Uplift:
+5-8 mm
GP
S V
elo
city
Tre
nd
s
1996 1998 2000 2002 2004 2006 2008 2010 2012 2014
0
50
100
150
200
250
300
DUND
Heig
ht
Tre
nd
[m
m]
Time [years]
DUNT
OUS2
OUSD
MQZG
LYTT
AVLN
WGTT
WARK
WGTN
TAKL
AUCK
Auckland
Wellington
Lyttelton
Dunedin
Velocity (mm/yr)
GPS SSE/EQ Local Sum
Auckland -0.6 -0.6
Wellington -3.0 +1.0 +1.0 -1.0 SSE velocity averaged over
15 years
Lyttelton -0.5 -0.3 -0.8
Dunedin -1.2 +0.5 -0.7
Earthquake coseismic
displacement averaged over
time series
Vertical Land Motion
Sea Level
Velocity (mm/yr)
RSL GPS SSE/EQ Local Sum Corrected
Auckland +1.55 -0.6 -0.62 +0.93 ± 0.09
Wellington +2.14 -3.0 +1.0 +1.0 -1.12 +1.02 ± 0.19
Lyttelton +1.98 -0.5 -0.3 -0.84 +1.14 ± 0.19
Dunedin +1.36 -1.2 +0.5 -0.67 +0.69 ± 0.20
Mean : +1.7 +0.9 ± 0.16
Summary
• New Zealand’s RSL is consistent with global trends: +1.7 mm/yr
• VLM needs to be taken into account • Local motion – levelling
• Regional motion – continuous GPS/GNSS
• NZ’s earthquake events appear to have a significant effect • WGTT : uplift is periodically caused by SSEs
• LYTT : post-seismic deformation caused by ChCh events
• DUNT : post-seismic deformation caused by (far-field) Fiordland events
• Evidence sites are uplifting/subsiding <~1 mm/yr
• Unclear what the long term effects of seismic activity are