Skip to content

Model vs reality

The question: does the simulation reproduce the range of deformation we measure after real earthquakes?

The dense cloud is the simulation set — 3,434 two-dimensional distinct element method (DEM) experiments, in which a modelled fault is pushed until the ground above it deforms. Scarp height is on the vertical axis, deformation zone width on the horizontal. Overlaid on it are measurements from real surface ruptures.

The paper's finding is that the simulations "comprehensively describe the range of historic surface rupture observations" in the field compilation.1

Unfamiliar terms?

Hover any acronym for its expansion. For fuller definitions: scarp, deformation zone width, hanging wall and footwall, scarp classes, and the field compilations FDHI and SURE.

Two quantities carry the comparison, both produced by the paper's computer-vision measurement model:2

  • Scarp height — the total height of the scarp, measured from the top of the undeformed footwall. For pressure ridges it exceeds the undeformed hanging-wall surface, because folding and uplift from secondary faults add to it.
  • Deformation zone width (DZW) — measured from the first vertical displacement seen in the hanging wall (uplift, tensile fractures or collapse) across to the base of the scarp in the footwall. It is a span across the disturbed zone, not a one-sided distance from the fault trace.

The model and field quantities are analogous, not identical

This is the paper's own caveat, and it matters for reading the overlay. The field compilation records fault zone width and vertical separation, measured in the field by different means than the model's DZW and scarp height. The paper states that because the compilation has no measurements of both scarp height and FZW for individual thrust and reverse events, it assumes "the measured vertical separation is similar enough to the scarp heights to foster these comparisons", citing the compilation's own report in support.3 The overlay rests on that assumption rather than on identical measurement.

The dashboard pairs the scatter with an event map, so you can see which earthquake each overlaid point came from and where it happened.

The model and field points are drawn as two separate layers. The DEM cloud carries the colour encoding, and a Color By control switches it between source/event, fault dip and scarp class; the field overlay is drawn as distinct shapes keyed to the event, and keeps that encoding whatever Color By is set to. Scarp class is a model classification in any case — the field measurements do not carry one.5

Colouring by scarp class splits the cloud into the six shapes the simulations produce: Monoclinal and Pressure Ridge — an inclined slope and a raised ridge respectively — Simple, where the fault offsets the surface directly, and a … Collapse variant of each, where the oversteepened face gave way. To see each of the six as the model draws it and as it looks in the field, open Figure 2; the two axes here are defined in Figure 5.

Open full-size on Tableau Public

Viable combinations

The same workbook carries a second view: a coverage matrix. Pick any two of source, event, scarp class, fault dip, cohesion or DEM set for the rows and columns, and each cell is shaded by how many measurements fall into that pairing — from none, through sparse, to dense.

It is worth a look before drawing conclusions from any slice of the cloud above, because a sparse or empty cell tells you the comparison in that region rests on very little data. What it does not tell you is why: an empty cell may be a combination the experiment set never covered, or simply one no observed earthquake happens to occupy.

Open full-size on Tableau Public

Where this comes from

This dashboard is the interactive form of chart family 1 in the project's own inventory, which maps it to the scatter panels of the paper's Figure 13.4

What feeds this dashboard

Both views read the unified_observations export — the cross-source table that normalises DEM, FDHI, SURE and Kern measurements onto shared columns. Its field slice is deliberately small: this is the scatter-overlay subset, not the full measurement population used by the per-event boxplots.5 The datasets themselves are described on the Data page.

Where to go next

  • Response curves — stay inside the simulations and watch each measurement grow as slip accumulates.
  • Per-event boxplots — the same model-versus-field comparison, but summarising each earthquake's spread rather than plotting every point.
  • Slip regression — the law linking slip to uplift, and what slip explains Kern County's measured displacement.
  • Glossary — what scarp height, DZW and scarp class actually mean.

Please cite as:

Chiama, K., Bednarz, W., Moss, R., Plesch, A., and Shaw, J. H. (2025). "Quantifying relationships between fault parameters and rupture characteristics associated with thrust and reverse fault earthquakes." Earthquake Spectra, 41(5), 3977–4014. DOI: 10.1177/87552930251346434

If you use the underlying data itself, cite the archives it comes from as well — the DEM experiments are deposited open-access on DesignSafe-CI, and the field compilations carry their own citations. The full list, with DOIs, is under How to cite this data.

Any DOI issued for this site or its source code identifies the software and the website, and does not replace the citations above.

Related work, for the wider project's 3D models — not a source for anything shown here:

Chiama, K., Plesch, A., and Shaw, J. H. (2025). "Along-Strike Variability of Surface Deformation on Thrust and Reverse Fault Ruptures: Insights from 3D Distinct Element Method Models." Seismological Research Letters 96(6), 3473–3489. DOI: 10.1785/0220250173

  1. Chiama et al. (2025), abstract. ↩

  2. Chiama et al. (2025), measurement methods; the paper's Figure 5 defines these quantities on the model geometry. ↩

  3. Chiama et al. (2025), section comparing DEM results with the FDHI dataset. ↩

  4. notes/chart-families.md in the source repository — a taxonomy of every figure in the paper and the legacy analysis notebooks, grouped by the question each chart answers. ↩

  5. notes/dashboard-3-build-spec.md in the source repository. ↩↩