SpecMod

A Python toolbox for processing and modelling seismic spectra, following the method of Edwards et al. (2010).

SpecMod estimates source parameters — long-period spectral level Ω, corner frequency f_c, and the attenuation operator t* — by fitting a Brune-type source model to direct-phase spectra.

Status: alpha, and under active reconstruction. The package is pre-1.0 and mid-refactor. The modern layers (specmod.config, specmod.core, specmod.transforms, specmod.picks, specmod.fitting) are built and tested; the older pipeline modules still carry pre-refactor behaviour and are being replaced stage by stage. Expect breaking changes at every 0.x release until the API settles at 1.0 — they land in minor bumps by design, with no deprecation cycle. Pin an exact version for anything you intend to publish. docs/roadmap.md says which stages are done and what 1.0 will mean; docs/REFACTOR_PLAN.md is the working document behind it.

Installation

Requires Python 3.11 or newer.

pip install -e ".[dev]"

Optional extras:

No Fortran compiler is needed. Multitaper estimation is implemented natively on SciPy's DPSS tapers, so the historical mtspec dependency — Fortran source with no wheels and no release since 2016 — is no longer required.

Estimating a spectrum

Every estimator returns a Spectrum that knows its own units:

import numpy as np
from specmod.transforms import FFTEstimator, MultitaperEstimator

dt = 0.01
trace = np.random.default_rng(0).normal(0, 1e-6, 2000)

spectrum = MultitaperEstimator(time_bandwidth=3.0, n_tapers=5).estimate(
    trace, dt, motion="velocity"
)

spectrum.unit           # 'm/s*s' — a Fourier amplitude spectrum
spectrum.duration       # 20.0 s, the physical record length
spectrum.energy()       # recovers sum(x**2) * dt

Conversions return new objects and are unit-aware:

spectrum.to_motion("displacement")   # divides by 2*pi*f
spectrum.to_kind("psd")              # A**2 / (2T)
spectrum.band(0.5, 25.0)

The wavelet estimator additionally exposes the full time-frequency surface, which is what to look at when a fit comes out wrong:

from specmod.transforms import CWTEstimator

scalogram = CWTEstimator().scalogram(trace, dt)
scalogram.time_average()     # an ordinary Spectrum, fits like any other
scalogram.coi_coverage()     # how much of the window each frequency resolves
scalogram.qc()               # concentration, coda balance, resolved bandwidth

Which estimator to use, and what each one does to your data — including measured position-dependence and the variance-normalisation convention mtspec used — is set out in docs/choosing-a-transform.md, with a worked walkthrough in docs/notebooks/choosing-a-transform.ipynb.

Why the units are typed

A spectrum carries its ground-motion domain and amplitude convention as attributes rather than in module-level globals. The alternative is keeping those globals in sync by hand with however many times .inte() or .diff() has been called, where getting it wrong returns a wrong seismic moment with no error anywhere. Here it is a type error.

Amplitude normalisation is keyed off the physical record duration, never off the length of the frequency axis, so zero-padding refines the frequency grid and changes nothing else.

Reading picks

Arrivals are attached to traces by set_picks, which detects the format from the file rather than from its name:

import specmod.preprocess as pre

pre.set_picks(stream, "event.xml")

Everything obspy.read_events parses is read through one delegate — QuakeML, SEISAN Nordic, HypoDD, NonLinLoc, IMS/GSE bulletins — plus Snuffler marker files, plus delimited tables whose columns you name. A format registered with ObsPy's own plugin system is read here with no SpecMod-side registration at all.

Most formats supply less than a full sensor identity — a bare station code is common — so a pick matches a trace on the fields it states. A pick that fits several sensors is an error rather than a broadcast: a station's surface and borehole instruments differ only by location code and do not see the same arrival.

Adding a format, the column mapping for a picker's CSV, and the policies for duplicate picks and multi-event files are in docs/pick-formats.md.

Configuration

Settings are grouped by pipeline stage and resolved through five layers — package defaults, a committed specmod.toml, a gitignored specmod.local.toml, SPECMOD_* environment variables, then explicit arguments:

specmod config show      # resolved values, and which layer set each one
specmod config freeze    # emit TOML to commit alongside a result

Package defaults reproduce the behaviour that shipped before the refactor, so upgrading does not silently move anyone's numbers. A study pins its own values in a committed file — see studies/magna_2020_paper.toml, which transcribes the workflow of the Magna paper below.

Every output records the configuration that produced it, a hash of it, and the SpecMod version, so a locally-overridden run is still reproducible from its outputs.

Documentation

The full documentation — the pipeline with its equations, the estimator comparison, pick formats, and an API reference — builds with Sphinx:

uv pip install -e '.[docs]'
sphinx-build -b html docs docs/_build/html

docs/REFACTOR_PLAN.md is excluded from the built site on purpose: it is a working document that records decisions and the measurements behind them, not documentation for using the package.

Development

uv venv && uv pip install -e ".[dev]"
pre-commit install                 # both hook types; not optional
pytest                             # test suite
pytest --without-optional-extras   # as a default install and CI see it
ruff check src/ tests/ tools/      # lint
ruff format src/ tests/ tools/
mypy                               # strict on the rewritten modules

docs/development.md is the full guide — the repository mapped, every tool and CI check, the branch and commit conventions, and where development stops and releasing begins. AGENTS.md is the short version that binds AI coding sessions.

Run --without-optional-extras before pushing. A development environment with specmod[multitaper] installed will pass tests that a default install fails, and CI installs only [dev].

The mypy override list in pyproject.toml is the migration backlog: modules leave it as they are rewritten, and the target is an empty list.

Command-line entry points are built on click, including internal tooling — one convention across the whole surface.

Measured numbers in the docs

The documentation quotes a lot of measurements, and stale numbers are worse than no numbers. Every table that came out of a measurement is generated:

python tools/measure_docs.py show     # print the tables
python tools/measure_docs.py write    # refresh the docs in place
python tools/measure_docs.py check    # fail if any table is stale

tests/test_docs_are_current.py runs check, so a change that moves a published number fails the suite rather than quietly leaving the prose wrong. Measurements that read tutorial/data/events/ are slower and opt-in via --field; refresh those by hand after changing an estimator.

Releasing

Commit messages follow Conventional Commits, which is what makes the changelog and the version automatic: release-please opens a standing release pull request, and merging it creates the tag, the GitHub Release, the PyPI upload and the Zenodo DOI. Nothing is released until that merge. See docs/releasing.md, which also lists the repository settings that have to be turned on once.

References

Edwards, B., Allmann, B., Fäh, D., Clinton, J. (2010). Automatic computation of moment magnitudes for small earthquakes and the scaling of local to moment magnitude. Geophysical Journal International 183(1), 407–420. https://doi.org/10.1111/j.1365-246X.2010.04743.x

Holt, J., Whidden, K.M., Koper, K.D., Pankow, K.L., Mayeda, K., Pechmann, J.C., Edwards, B., Gök, R., Walter, W.R. Towards robust and routine determination of Mw for small earthquakes: application to the 2020 Mw 5.7 Magna, Utah, seismic sequence. Seismological Research Letters.

Thomson, D.J. (1982). Spectrum estimation and harmonic analysis. Proceedings of the IEEE 70(9), 1055–1096.

Contributing

Issues and pull requests are welcome. Commits follow Conventional Commits, which drives the changelog and version bumps.

License

MIT — see LICENSE.