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LAPOD 2.0 - Latin American Paleomagnetism Online Database

Filtering and visualization of paleomagnetic records

Institute of Geosciences, UNAM

Fold test

Bootstrap eigenanalysis of directional clustering during progressive unfolding

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Directional and bedding data

Enter geographic paleomagnetic directions and bedding attitude. The test progressively removes bedding tilt and tracks the maximum clustering of the directions.

Structural input uses dip direction and dip. If a text file contains Strike and Dip instead, dip direction is taken as Strike + 90Β° (right-hand-rule style).
The file is processed locally in your browser.
Recommended columnsID, Dec, Inc, DipDirection, DipAlternatively: ID, Dec, Inc, Strike, Dip.

Input data

No data loaded yet.
#IDDIDipDirDip

Fold-test settings

Primary clustering statistic: Ο„1, the largest eigenvalue of the orientation matrix. This metric is polarity-independent.

Fold-test result

Best unfoldingβ€”
95% bootstrap intervalβ€”
Ο„1 maxβ€”
Interpretationβ€”

Fold-test plots

Clustering versus unfolding
Bootstrap distribution of optimum unfolding
0% β€” Geographic
Best unfolding
100% β€” Stratigraphic
Equal-area Schmidt projections. Positive inclinations (down) are filled; negative inclinations (up) are open.

Methodological note

At each unfolding percentage, every direction is rotated about the bedding strike axis by the corresponding fraction of dip. The orientation matrix of the resulting unit vectors is calculated and Ο„1 is used as the clustering statistic.

Bootstrap resampling with replacement is then used to estimate the distribution and 95% interval of the unfolding percentage that maximizes Ο„1. Geological interpretation must still consider structural complexity, plunging folds, remagnetization, and bedding uncertainty.