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Processing Options

Particle Motion Analysis

The pm (particle motion) method analyzes the motion of a particle as recorded by a three-component seismic station (e.g., Z, N, E components). It provides geometrical parameters such as azimuth, incidence angle, rectilinearity, and planarity, which are critical for understanding wave polarization and propagation direction.

Description

Particle motion analysis plots the trajectory of ground motion in 3D (or in 2D projections like Z-N, Z-E, and N-E planes). By examining these plots, users can determine:

  • Azimuth (°): The horizontal direction of wave propagation.
  • Incidence (°): The vertical angle of wave arrival relative to the surface.
  • Rectilinearity: A measure of how straight (linear) the motion is, often associated with body waves.
  • Planarity: A measure of how planar (flat) the motion is, often associated with surface waves.

The method automatically detects and maps three-component combinations (e.g., ZNE, Z12, ZYX) and processes them accordingly.

Parameters

  • output_path (optional): Directory where particle motion plots and results will be saved.
  • If provided, a text file pm.txt will record azimuth, incidence, rectilinearity, and planarity for each analyzed trace.
  • A .png plot is generated for each station.

Config Example

Analysis:
  process_1:
    name: 'particle_motion'
    output_path: './pm_results'

Outputs

For each valid three-component station: - Plots: - Z vs. N projection - Z vs. E projection - N vs. E projection (with azimuth arrow) - Information box with computed parameters - Text file (pm.txt): Appends results in CSV format: 

NET.STA.LOC.CHAN, YYYY-MM-DD HH:MM:SS, Azimuth, Incidence, Rectilinearity, Planarity

Example Output Plot

The particle motion figure contains: 1. Z vs. N plane with incidence angle overlay. 2. Z vs. E plane with incidence angle overlay. 3. N vs. E plane with azimuth direction indicated by an arrow. 4. A summary panel showing: - Azimuth - Incidence - Rectilinearity - Planarity

Scientific Background

Particle motion analysis is widely used in seismology for polarization studies, wavefield separation, and source characterization. For more details, see:

  • Flinn, E. A. (1965). Signal Analysis Using Rectilinearity and Direction of Particle Motion. Proceedings of the IEEE, 53(12), 1874–1876.
  • Vidale, J. E. (1986). Complex polarization analysis of particle motion. Bulletin of the Seismological Society of America, 76(5), 1393–1405.

Notes

  • Ensure that three-component data are present for each station (ZNE or equivalent).
  • The traces are trimmed to a common time window before analysis.
  • If no valid 3-component set is found, the process is skipped for that station.