Sea level and post-seismic vertical movements

See installation Report pdf - html

The 12 January Haiti earthquake produced no surface rupture, consistent with Insar imagery and teleseismic inversion that suggest that rupture terminated 2-4 km below the surface. Three interpretations are possible: that slip in this 2 km shallow subsurface region occurred prior to the earthquake as aseismic creep, that slip is currently occurring in this region as afterslip, and that slip will be released in a future earthquake. The tide gauge measurements are designed to address the second two of these possibilities. The magnitude of this future earthquake would be Mw=6.5 if it consists of a 4x35 km patch of the Enriquillo fault that slips ≈2 m, or the apparent deficit could be released as part of a larger earthquake.

The Gonave Tide Gauge is attached to a siliceous limestone north of the village of Petite Gonave. The pressure gauge is mounted to the base of a steel bar bolted to bedrock.

The map shows the locations of five tide gauges installed after the 12 January earthquake. GONA is a reference site relative to which post seismic height changes are being measured. Click on the gauge name above or on the map itself for more details. GONA is described below. We thank DataGarrison com for the generous loan of the PARA Iridium transmitter, and for providing access to GONA, JACK and BLOC.

Sea level near Haiti is at its lowest since 1994 as a result of oceanic gyres in the Caribbean (TOPEX). The experimental measurements described here are designed to measure changes in relative elevation between reference gage GONA and four coastal sites near the epicenter of the Haiti earthquake. Results to May 2010 show adjustments of a few mm each week. The data are provided to the Ministry of Mines and Energy, Haiti, with whom we are collaborating.

Gonave (GONA) 18.704 N, 72.805 W

The tide gauge was installed 6 March 2010. Data are transmitted every 2 hours via the Iridium satellite. For the first few days instantaneous unfiltered samples were logged at 10 minute intervals (figure below). Thereafter the data were sampled every 44 s and digitally averaged before transmission at 15 minute intervals. Data displayed in local time (GMT-5 hrs) may be viewed at:

http://cires.colorado.edu/science/groups/bilham/haiti/

or alternatively data may be downloaded using the following procedure:

https://datagarrison.com/

user name geo, password hobo

click on Gonave, Haiti at bottom of page

A graphic display of data is shown with the top panel indicating all the data, and the lower panel indicating the last three days of data. Scale is in cm of sea level rise. Times are shown in local time (UTC-300 minutes).

At the top of the page click on Control Panel. You will see a list of data files. Click on the most recent Gonave file.

Now click on the words tab delimited . The file name you have selected is now displayed.

Now click on the file Gonave_xx.text. A listing of data are shown. The first file (xx) was 13, the second 14.

Now save the file to your computer (in Safari in an Apple Computer use Save As under file and the file wil be saved as a text file that can be opened in Excel.

Open Excel. Open file name. Choose delimited and it will automatically parse the file into three columns: Date, Sea Level in cm, and a column of no interest indicating battery health. Note that the dates in the ascii file are local time offset from UTC by the time indicated in the second line of the header (local time -5 hours). The data are shown in cm to three decimal places but only one is significant.

An installation report shows calibration information, installation details, and describes initial data quality.

First three days of 10 minute data (GMT-5) from Gonave (red line Gonave_013.txt) showing 20 minute seiche with amplitude 5-10 cm superimposed on 35 cm tide. Black line is 2 hour filtered data.

Example of filtered differenced sea level data from GONA, JACK, CIRA and PARA. The initial low signal at JACK was caused by a blockage in the pressure port.