Content-type: text/html Man page of magellan

magellan

Section: User Commands (1)
Updated: May 5th 2010
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NAME

magellan - Program to Model Marine Magnetic Anomalies

SYNOPSIS

magellan [options] [datafile]

DESCRIPTION

Magellan is a program that handles forward modeling of marine magnetic anomalies. It is based on computer program Talwani and others wrote in 1964 where the contribution to a magnetic field from a 2-d polygon is calculated. It can simulate ridge jumps, asymmteric spreading and varying magnetization. The output is a figure showing the synthetic magnetic field, the magnetic anomaly data (if applicable) and the arrangement of the magnetized blocks. Magellan uses bathymetry to assume the shape of the magnetized blocks.

DATA FILE

The data file is an ascii file with five columns, distance lat lon depth anom, where distance is distance from the ridge in kilometers, lat is the latitude of the data, lon is the longitude of the data, depth is the (positive) depth in kilometers and, anom is the magnetic anomaly (in nT). In the configuration file, the data file can be set with the data key, i.e. data=filename.

OPTIONS

-a filename --asymmetry=filename

A file containing the asymmetry used in the modeling. In the configuration file, the asymmetry file can be set with the asymmetry key, i.e. asymmetry=filename. The format of the asymmetry file is start end asymmetry where start and end are the beginning and end of the time interval of the asymmetry in Myr (million years) and asymmetry is a percentage represented as a fraction (i.e. 0.03) during that time interval. A negative number represents faster spreading in the left direction, and a positive number represents faster spreading in the right direction (left being the westerly part of the profile and right being the easterly part). For instance if the asymmetry is 0.05 the spreading rate to the left of the ridge is (1 - 0.05) * 1/2 spreading rate and to the right of the ridge the spreading rate is (1 + 0.05) * 1/2 spreading rate. Thus, when the left and right spreading rates are added, the outcome is always the full spreading rate.

-j filename --jump=filename

A file containing the jump(s) used in the modeling. In the configuration file, the jump file can be set with the jump key, i.e. jump=filename. The format of the jump file is time jump, where time is the time when the jump occurs in Myr (million years) and jump is the distance of the jump in kilometers. Negative and positive jumps represent ridge jumps where the new ridge forms left and right of the current ridge, respectively.

-s filename --spreadingrate=filename

A file containing the spreading rate(s) used in the modeling. In the configuration file, the spreading rate file can be set with the spreadingrate key, i.e. spreadingrate=filename. The format of the spreading rate file is start end rate, where start and end are the beginning and end of the time interval in Myr (million years) and rate is the total spreading rate in km/Myr (kilometers per million years) of the ridge during that time interval. Unless an asymmetry file is specified the spreading of the ridge is symmetric with both sides of the ridge spreading at half the spreading rate.

-m filename --magnetization=filename

A file containing the magnetization used in the modeling. In the configuration file, the magnetization file can be set with the magnetization key, i.e. magnetization=filename. The format of the magnetization file is start end magnetization, where start and end are the beginning and end of the time interval in Myr (million years) and magnetization is the magnetization in A/m (amperes per meter) during that time interval.

-t filename --timescale=filename

A file containing the time scale used in the modeling. In the configuration file, the time scale file can be set with the timescale key, i.e. timescale=filename. The format of the time scale file is start end, where start and end are the beginning and end of the time interval in Myr (million years). The time scale of Cande and Kent (1995) is used as a default, so if this option is not set Cande and Kent is used.

-b degrees --profile_azimuth=degrees

The azimuth of the profile, measured clockwise from the north. In the configuration file, the azimuth can be set with the profile_azimuth key, i.e. profile_azimuth=amount. Default is profile_azimuth=90.

-d degrees --declination=degrees

The declination used in the modeling. In the configuration file, the declination can be set with the declination key, i.e. declination=amount. Default is declination=45.

-i degrees --inclination=degrees

The inclination used in the modeling. In the configuration file, the inclination can be set with the inclination key, i.e. inclination=amount. Default is inclination=45.

-k value --contam=value

The contamination coefficient suppresses higher frequency in the model. See manual for further information. In the configuration file, the contamination coefficient can be set with the contam key, i.e. contam=value. Default is contam=1.

-z thickness --thickness=kilometers

Thickness of the magnetized layer in kilometers. In the configuration file, the thickness can be set with the thickness key, i.e. thickness=amount. Default is thickness=0.5.

-o degrees --spreading_direction=degrees

Current spreading direction of the ridge. In the configuration file, the spreading direction can be set with the spreading_direction key, i.e. spreading_direction=amount. Default is spreading_direction=90.

-r degrees --ridge_azimuth=degrees

The azimuth of the ridge. In the configuration file, the ridge azimuth can be set with the ridge_azimuth key, i.e. ridge_azimuth=amount. Default is spreading_direction=0.

-p distance --pointspacing=distance

The spacing between points in kilometers when the model is calculated. In the configuration file, the spacing between points can be set with the pointspacing key, i.e. pointspacing=amount. Default is pointspacing=1

-h --help

Print a small help text explaining the usage of magellan briefly.

-c filename --config=filename

A configuration file which defines basic input into magellan.

EXAMPLES

Spreading Rate File Example

% Everything written after the percentage sign is a comment
% This is a plain text file with the format below
% start(Myr) end(Myr) full spreading rate(km/Myr)
0 50 20 
50 89 25
89 118 15

Asymmetry File Example

% Everything written after the percentage sign is a comment
% This is a plain text file with the format below
% start(Myr) end(Myr) asymmetry(%)
0 50 0.04 
50 89 0.01
89 118 -0.02

Jump File Example

% Everything written after the percentage sign is a comment
% This is a plain text file with the format below
% time(Myr) distance(km)
3 4.3
23 -3.1

Magnetization File Example

% Everything written after the percentage sign is a comment
% This is a plain text file with the format below
% start(Myr) end(Myr) magnetization(A/m)
0 0.78 20 
0.78 10 10 
10 118 5

Time Scale File Example

% Everything written after the percentage sign is a comment
% This is a plain text file with the format below
% start(Myr) end(Myr)
0 10
10 50 
50 118

Configuration file

% Everything written after the percentage sign is a comment
% This is a plain text file with the format below
thickness=1
inclination=75
declination=-18
obliquity=30
spreadingrate=track22.spr
asymmetry=track22.as
magnetization=track22.mag
jump=track22.jump
data=track22.xzm
timescale=mytimescale
contam=0.7

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Time: 09:17:53 GMT, May 06, 2010