PySurf96

Modelling Surface Wave Dispersion Curves

This is a slim wrapper around the program surf96 from Computer programs in seismology by R. Hermann (http://www.eas.slu.edu/eqc/eqccps.html) for forward modelling of Rayleigh and Love wave dispersion curves.

In this realisation the Fortran77 code is wrapped by f2py, which makes the forward computation approximately 8x faster compared over calling a Python subprocess.

More useful software for seismology at https://pyrocko.org.

Installation

This package is for Python 3.

Prerequisits is a Fortran77 compiler, like GNU GCC.

pip3 install .

Or through pip:

pip install git+https://github.com/miili/pysurf96

Documentation

Essentially this is a single function, surf96. Here is the docstring:

Calculate synthetic surface wave dispersion curves for a given earth model, wave type and periods.

This is a slim Fortran wrapper around surf96 from Computer Programs in Seismology from R. Hermann (2013)

Args:
    thickness (np.ndarray): Layer thickness in kilometers.
    vp (np.ndarray): Layer Vp velocity.
    vs (np.ndarray): Layer Vs velocity.
    rho (np.ndarray): Layer density in g/m^3.
    periods (np.ndarray): The periods in seconds, where wave velocity is calculated
    wave (WaveType, optional): The wave type, "love" or "rayleigh". Defaults to "love".
    mode (int, optional): Mode of the wave, 1: fundamental, 2: second-mode, etc... Defaults to 1.
    velocity (Velocity, optional): "group" or "phase" velocity. Defaults to "group".
    flat_earth (bool, optional): Assume a flat earth. Defaults to True.
Raises:
    ValueError: Raised when input values are unexpected.
    Surf96Error: If surf96 fortran code raises an error,
        this may be due to low velocity zone.
Returns:
    np.ndarray: The surface wave velocities at defined periods.

Example

import numpy as np
from pysurf96 import surf96

# Define the velocity model in km and km/s
thickness = np.array([5.0, 23.0, 8.0, 0])
vs = np.array([2, 3.6, 3.8, 3.3])
vp = vs * 1.73
rho = vp * 0.32 + 0.77

# Periods we are interested in
periods = np.linspace(1.0, 20.0, 20)

velocities = surf96(
    thickness,
    vp,
    vs,
    rho,
    periods,
    wave="love",
    mode=1,
    velocity="group",
    flat_earth=True,

Citations and Acknowledgments

Herrmann, R. B. (2013) Computer programs in seismology: An evolving tool for instruction and research, Seism. Res. Lettr. 84, 1081-1088, doi:10.1785/0220110096

Thanks to Hongjian Fang for creating the Fortran subroutine (https://github.com/caiweicaiwei/SurfTomo)