GPS geodesy: applications to geosciences

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GPS geodesy applications to geosciences
case overview

• Puerto Rico-Virgin Islands microplate
• Soufriere Hills volcano, Montserrat
• Nicaragua forearc deformation
• New Madrid Seismic Zone

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CASE 1
GPS results from Puerto Rico and the Virgin
Islands Constraints on microplate tectonics
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overview
general tectonics of Caribbean plate model
for northeastern Caribbean Caribbean reference
frame microplate tectonics in northeastern
Caribbean deformation across Puerto Rico and
the Virgin Islands
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What is societal interest in the research?
SEISMIC HAZARD! Why is it important in
Puerto Rico?
probability of various ground motions in
specified time
USGS curves equate San Juan, Mayagüez with Seattle
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population density of Puerto Rico 1,124 per
square mile
if US had same population density as Puerto Rico.
population of US would be 3 billion
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circum-Caribbean seismicity (defines plate)
Caribbean
epicenters lt 30 km depth from USGS
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Caribbean bathymetry
BR Beata Ridge HE Hess Escarpment NPDB North
Panama Deformed Belt SCDB South Caribbean
deformed belt
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depth to slab
NOAM subducts westward below Caribbean
along Lesser Antilles
http//www.ig.utexas.edu/research/projects/venez_m
argin/venez_margin.htm
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positions of the leading edge of Caribbean plate
in the past i.e. where subduction was
http//www.ig.utexas.edu/research/projects/venez_m
argin/venez_margin.htm
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bathymetry around the corner
note Bahamas colliding with Hispaniola
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North American-Caribbean plate boundary
MC Mona Canyon AP Anegada Passage MT
Muertos trough
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proposed microplates of the northeastern Caribbean
from west to east Gonave Hispaniola Puerto
Rico-Virgin Islands (PRVI)
(modified from Mann et al., 1995)
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bathymetry offshore Puerto Rico and Virgin Islands
from http//www.vangestel.com
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block-faulting west of St. Croix
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profiles across Puerto Rico
from http//www.vangestel.com
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models for Puerto Rico-Virgin Islands microplate
.Caribbean moves east relative to
NOAM. left-lateral strike-slip along northern
boundary
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40 CCW since Eocene 12 CCW since Miocene
0 last 2 m.y.
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seismicity mostly offshore supports rigidity of
PRVI thrust events along western MT and eastern
PRT support rotation little seismicity along AP
provides no constraint setting of western PRT
isnt clear
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GPS geodesy in northeastern Caribbean 1986
(NASA) 6 sites 1994 (NSF)
6 original sites plus new sites in Hispaniola,
Puerto Rico and British Virgin Islands
1995 to present (NSF NASA) expansion
of network throughout Hispaniola (Calais),
Puerto Rico, Virgin Islands (Jansma,
Mattioli)
occupations of subsets of sites done yearly since
1995
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definition of Caribbean reference frame
most of the islands sit on edges of the plate
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interior of plate has lots of ocean, not much land
one spot in eastern CaribbeanAves Island
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sites for Caribbean reference frame (stars)
DeMets et al. (2000) AVES, SANA, ROJO, CRO1
plus transforms currently, we use this
plus BARB (unpublished)
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best fit NOAM-CARIB rate
19 mm/yr ENE azimuth
twice as fast as NUVEL-1A azimuth N70E at PR
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problems with Caribbean reference frame

• too few sites
• time series too short (noise significant) for key
  sites (AVES)
• potential that Caribbean is TWO plates and/or
  deforming

potential improvements

• additional sites in Honduras, Nicaragua, Lesser
  Antilles
• additional occupations (AVES for
  March--volunteers?)

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too few sites
Nicaragua
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can use BARB (already do) FSDO
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other sites in Lesser Antilles also may be on
stable Caribbean . too early to tell
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only 2 occupations
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Caribbean deformation? (affects reference frame)
two plates western (SANA) and eastern (AVES)
plates
little seismicity in interior says no some
features suggest maybe
we know that NOAM and SOAM are converging
subduction of Caribbean below Muertos Trough
and South America
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GPS network in northeastern Caribbean
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potentially active faults on Puerto Rico
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data from continuous GPS sites (ITRF00)
western Puerto Rico
eastern Puerto Rico
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data from campaign GPS sites (ITRF00)
western Puerto Rico
eastern Virgin Islands
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do separate microplates exist?yes
clear difference between Hispaniola and Puerto
Rico extension of 5 mm/yr across Mona rift
Hispaniola moves rapidly relative to Caribbean
(slowly wrt NOAM) PRVI moves slowly relative to
Caribbean (rapidly wrt CARIB)
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does Puerto Rico rotate?no
component of convergence across western Puerto
Rico trench not compatible with rotation
model similar azimuths of velocities
throughout Puerto Rico not compatible with
rotation about nearby vertical axis
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does Puerto Rico escape to east? have active
faults?
island moves at 85 of total CARIB plate rate
wrt NOAM Virgin Gorda has no motion wrt CARIB
(no tectonic escape) increasing velocities
westward across PRVI (EW extension) velocities
for western PR sites are similar (faults?)
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The Dynamics of an Ongoing Andesitic
Eruption What we have learned from Surface
Deformation at Soufriere Hills, Montserrat, BWI
CASE 2
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eruption began in July 1995 as phreatic
(steam) became phreato-magmatic in October
1995 explosions began in September 1996
initial GPS occupations began in August 1995
L1 only receivers early campaigns with dual
frequency receivers began October 1995
continuous GPS in summer 1996
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data from August 1995-October 1996
note large error bar on circle (L1 measurement)
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Tar River Valley - Looking ENE October 1995
English Crater 4 Ka Sector Collapse
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GPS analysis strategy

• Campaign and continuous GPS geodesy done from
  1995-2002
• Several CGPS sites destroyed over the years
  current network is 6 sites - Choke Ring Antennae
  with UNAVCO radomes and FreeWave RF telemetry
• Data processed in absolute point positioning mode
  with final JPL orbits, clocks, and earth
  orientation parameters - Time series in ITRF97
  and the referenced to fixed CAR (DeMets et al.,
  2000)
• GPS velocities are modeled assuming linear
  segments for each of three periods

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No Surface Flux
Renewed Dome Growth
Explosions -gt
lt-Dome Growth
Subsidence Again! -gt
lt- Subsidence
Inflation -gt
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