[lispandfound]

Summary

Adds depth-dependent ("hybrid") slip correlation lengths, after Graves & Pitarka's SCEC 2026 poster GM-218 and genslip v5.6.3 (SCEC BBP dev branch). Shallow slip can use long correlation lengths (Suzuki et al. 2022) and deep slip short ones (Mai & Beroza 2002), crossfaded between two depths. It also supports any number of families.

GP blends two fields linearly, so the latent variance drops in the transition, to 0.845 at Mw 7 with shared noise and 0.5 with independent noise. This PR blends in quadrature instead:

• Every family filters one shared white noise, embedded on a common padded grid.
• Families are crossfaded at equal power: loading sin(πw/2), normalised by the exact cross-correlations between families. The latent field is therefore standard normal at every cell, and the marginal transform stays exact.

The structure was settled through two architecture reviews, a devil's-advocate pass, /simplify and /code-review. Backwards compatibility was explicitly not a constraint.

Changes

• sampling/field.py: one Sampler type for any number of covariances. sampler(grid, covariances, weights=None) embeds them at the widest padded shape and draws all of them from one seed. The stationary case is one covariance. The lru_cache on sampler is gone.
• rupture/models.py:
  • NoiseFamily(relation, hurst, weight), with Noise = tuple[NoiseFamily, ...] and STATIONARY as the default noise.
  • embed(noise, geometry, magnitude, marginal) pre-corrects each family for the marginal, reads the weights at cell centres, and caches the result.
  • DrawnSlip.noise, GaussianRake.noise and CorrelatedPerturbation.noise let each model choose its noise. Making rake hybrid is a config change. By default rake stays stationary and the perturbation uses slip's noise, which matches genslip's slip and rake. genslip keeps the perturbation's own part stationary; set perturbation.noise to STATIONARY to reproduce that.
  • SlipField.sampler replaces latent_covariance. Rise time and the onset perturbation draw their independent part from slip's built sampler, so nothing is embedded twice.
• rupture/source.py:
  • SegmentSource is now a moment and a rake, with a magnitude property.
  • CorrelationRelation gains strike_saturation and dip_saturation, for SEA22's min(Mw, 6.3).
  • New SUZUKI_2022 relation.
• config.py: [[slip.noise]], [[rake.noise]] and [[perturbation.noise]] replace [source.correlation] and [segments.<name>.correlation]. A segment's noise list replaces the global one whole. Profile depth/value lists are now tuples, so profiles are hashable.
• Examples and README are updated to match.

Breaking changes (intentional)

• Configs with [source.correlation] no longer load. The lengths now live on each model's noise.
• SegmentSource.covariance, SlipField.latent_covariance, segment_source's correlation arguments, and sampler.cache_clear() are removed. The cache is now embed.cache_clear().
• Draws differ slightly from before, because stationary fields are now normalised exactly for clipped eigenvalues.

Example

[[slip.noise]]   # shallow: Suzuki et al. (2022)
relation = { strike_offset = 1.67, dip_exponent = 0.5, dip_offset = 1.69, dip_saturation = 6.3 }
weight = { type = "ramp", centre_km = 6.5, half_width_km = 1.5, shallow = 1.0, deep = 0.0 }

[[slip.noise]]   # deep: Mai & Beroza (2002), the default relation
weight = { type = "ramp", centre_km = 6.5, half_width_km = 1.5, shallow = 0.0, deep = 1.0 }

Testing

• pytest tests: 247 passed, 1 skipped.
• Doctests, ruff and ty pass; ty only reports the existing unresolved rerun import.
• pytest benchmarks/test_kernels.py --benchmark-disable passes.
• New tests/test_blend.py covers:
  • saturation;
  • the shared padded shape;
  • a cell under one family equalling that family's own draw;
  • empirical unit variance and independent real and imaginary parts through the crossfade;
  • weight validation;
  • slip versus rake noise ownership;
  • the perturbation's own noise;
  • config round trip and segment overrides.

Not in this PR

• GP's depth-dependent along-strike side taper (taper_slip_all_r_hc).
• A Rust kernel that generates the white noise once for all K transforms.
• Draws with several families cost K transforms on the largest family's padded grid. At Mw 7 with SEA22 that is about 23× the stationary MB02 cost.

---

Generated by Claude Code

[github-actions]

Benchmarks

3736a8c against base 36a8c4a, on AMD EPYC 9V45 96-Core Processor. Times are medians over the rounds. The median change is 2.8%; changes past 5% are in bold.

Kernels

kernel	base	head	change	head IQR	rounds	padded cells
embed[Mw6.5]	26.1 ms	26.3 ms	+1.0%	472 µs	34	448,000 (+0.0%)
circulant_draw[Mw6.5]	2.36 ms	2.52 ms	+6.6%	221 µs	282
embed[Mw7.5]	84 ms	84.5 ms	+0.6%	1.39 ms	12	1,204,224 (+0.0%)
circulant_draw[Mw7.5]	5.54 ms	5.73 ms	+3.4%	471 µs	158
eikonal_solve	909 ms	939 ms	+3.3%	21 ms	5
synthesise_pulses[impulse]	358 µs	359 µs	+0.5%	18.1 µs	1307
synthesise_pulses[liu]	322 ms	331 ms	+2.7%	8.96 ms	5

End to end

Each round is the command line in a fresh interpreter, start-up included. Peak RSS is the largest the child process reached over the rounds.

example	base time	head time	change	base peak RSS	head peak RSS	change
alpine_hope	6.24 s	6.21 s	-0.5%	294 MiB	301 MiB	+2.3%
beavan	2.26 s	2.31 s	+1.9%	232 MiB	234 MiB	+0.8%
colombia	5.9 s	5.99 s	+1.6%	3,170 MiB	3,175 MiB	+0.2%
crustal	918 ms	975 ms	+6.2%	246 MiB	247 MiB	+0.5%
landers	1.84 s	1.9 s	+3.6%	386 MiB	389 MiB	+0.8%
northridge	889 ms	916 ms	+3.0%	289 MiB	290 MiB	+0.6%
two_faults	1.58 s	1.64 s	+3.9%	355 MiB	357 MiB	+0.6%
two_faults_segments	920 ms	968 ms	+5.3%	191 MiB	193 MiB	+1.2%
venezuela	12.1 s	11.8 s	-2.0%	5,768 MiB	5,789 MiB	+0.4%