Study Tour

Gravity: A Dominant Force In The Universe

Pre-generals students are required to carry out a research project related to this year’s theme - preferably something outside their current field of research.  They will be required to write this work up in an 8-10 page report, due at our last class meeting.  In addition, they will give a 12-15 minute oral presentation at the end of the course, reporting the results of their findings.

Some  project ideas that were solicited from seminar quest speakers, WHOI staff and falculty are presented below.  Please notify this year's science organizers (Steve or Pablo) if you'd like to carry out one of these projects.

1. David Sandwell (dsandwell@ucsd.edu)

I would be happy to help students on their term projects with a focus on the following two topics:

1) Prediction of bathymetry from satellite and ship data. http://topex.ucsd.edu/sandwell/publications/111.pdfhttp://topex.ucsd.edu/sandwell/publications/79.pdf

2) Gravity field construction from satellite altimetry. http://topex.ucsd.edu/sandwell/publications/122.pdf

2. Rob Sohn (G&G)

Potential project: Space-time variations in surface tilt related to fluid flow and eruptions at the Lone Star geyser, Yellowstone.

This project will focus on analyzing tiltmeter data acquired from the Lone Star geyser in Yellowstone National Park for 5 days in 2010. The data were acquired at 5 stations on the geyser sinter cone, along with simultaneous broadband seismometer, gravimeter, FLIR, LIDAR, and stream discharge measurements. The tilt data are noisy, but they contain signal related to poroelastic pressure variations and fluid movement inside the geyser plumbing system. Signal processing to remove the noise will constitute an important part of this project. Once the noise is removed the data can be rotated for each station to determine how the ground surface displaces in response to subsurface pressure changes. Depending on the complexity of this signal, it may also be possible to develop simple analytical models of subsurface processes.

3. Ralph Stephen (G&G)

Title: Ocean Bottom Seismometer Observations of Surface Gravity Waves

This project involves analyzing broadband ocean bottom seismometer (OBS) data over a ten day period in the Philippine Sea.  During this period winds went from near zero to 50km/hour as a typhoon passed over the sensors and then returned to near zero.  OBSs are very sensitive to vibrations due to the ocean surface gravity waves excited by local winds as well as vibrations from storms and gravity waves incident on distant coastlines.   This is a unique data set because in addition to five OBSs there was a vertical line array of hydrophones extending up to a kilometer above the seafloor.  This enables us to distinguish sound coming from directly overhead from sound propagating along the seafloor.  Good Matlab skills and a knowledge of fundamental signal processing are essential.

4. J. Pablo Canales (G&G)

Project Title: Gravity Anomalies at the East Pacific Rise

Project Description:  This project will consist of processing and reducing shipborne marine gravity data collected across the East Pacific Rise along closely spaced survey profiles.  Specific steps will include: (1) merging time-series raw gravity measurements with navigation data; (2) reduction of raw gravity measurements to free-air anomalies; (3) filtering and cleaning; (4) gridding; (5) calculation of mantle Bouguer anomalies; (6) geological interpretation.  Completion of steps 1-4 will be sufficient to receive credit for this project.  If the student is interested, he/she will be able to continue with steps 5-6, which can potentially result in a General’s project if needed.

Basic knowledge of MATLAB and time-series analysis (e.g., Fourier transform, filtering, etc.), as well as manipulation/display of serial and geographical data (e.g., GMT), is recommended.

5. Masako Tominaga (G&G) with Maurice Tivey (G&G) and James Kinsey (AOP&E)

Project Title: Marine Gravity Study of the nature of the Old Pacific Crust

Project Description:  The data were collected by a BGM-3 shipboard gravimeter during our recent Hawaiian Jurassic cruise. Our trackline covers the ground from the port of Oahu, crossing Necker Ridge and Mid-Pacific Mountains, to ~ 145 Ma Pacific crust into the oldest part of the Pacific basin (the birth place of the Pacific ocean), then to Guam after crossing Marianas Trench. The data set (gravity, shipboard multibeam and echosounder data for bathymetry) is invaluable since no cruise has collected such comprehensive geophysics data from this part of the Pacific basins.

The project will be two fold:

1. the most of the gravity data from this cruise were already reduced except for 48 hrs worth of data. A student will first finalize this remaining part of the raw gravity data reduction as well as applying the instrument drift from gravity-tie for the whole data set in order to learn (A) marine gravity basics, (B) potential field theory, and (C) simple computational skills (MATLAB).

2. once the student will obtain the entire gravity and topographic information, s/he will conduct forward modeling to detect crustal thickness, especially around seamounts, over the "bulge" along the NE_SW long track lines, and over Marianas Trench. Comparison between the satellite predicted gravity model and ship gravity will be interesting to understand various gravity measurement systems available today. To interprete the data, the student will learn marine geology and geodynamics of the Pacific basins especially about the history of mid-ocean ridge systems that formed old Pacific basins and Marianas Trench.

The success of this small project will add student's name as one of the co-authors on an AGU Fall meeting poster in future.

I and Maurice (PIs of the cruise) will supervise the student. James Kinsey will provide a short lecture on technical/engineering aspects of marine gravity instrumentation and data acquisition to broaden our understanding of where/how gravity data are from.

6. Jeff McGuire (G&G)

Title:  Gravity Changes During the Seismic Cycle?

Faults on land have been shown to have measureable time-dependent gravity signals resulting from fluid flow.  A first order question is how the fluid content of the fault-zone varies over the earthquake cycle on a given fault.  Oceanic Transform faults could be an advantageous location to study time-dependent anomalies in the gravity field because they have very short seismic cycles (5-10 years) and there is strong evidence that the porosity in the fault-zone is strongly time dependent.  This project will seek to determine if any time-dependent anomalies are resolveable in the TOPEX data where the tracks cross a few East Pacific Rise transform faults with short seismic cycles.