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A fold with older layers in its core where the age relationships are preserved. Active blind reverse faults can produce asymmetric anticlines and warping of young landforms.

A fold formed as displacement is transferred ahead of a propagating fault tip into surrounding rock. It is one mechanism for surface deformation above a blind reverse fault.

Relative movement parallel to bedding during folding, allowing layers at different radii of curvature to accommodate different arc lengths. For two layer surfaces separated by thickness $h$ through bend angle $\theta$, their arc-length difference is approximately $h\theta$. Bedding-parallel slip can accommodate that mismatch without requiring each layer to stretch by the same amount. Shallow flexural slip can produce surface breaks above a blind reverse fault.

A topographic step or steepened belt produced by localized folding. It can form above a blind reverse fault without being the trace of the principal fault plane.

A blind reverse fault can shorten and bend its cover into a fault-propagation fold or other growing anticline. At the fold crest, bending can create shallow extension and secondary normal faults or tension fissures, even though the regional deformation is shortening. Bedding-parallel flexural slip, local backthrusts and fold scarps can also break the surface.

Thus a shallow surface break need not be the upward continuation of the main seismogenic thrust fault. The expected association is distributed deformation related to the uplifted fold; its detailed pattern depends on cover layering, fold geometry and shallow strength. The broad frontal relief in Attachment A is compatible with this possibility, but the image alone does not establish a unique earthquake rupture history.

After removing orbital, topographic and atmospheric contributions, an earthquake InSAR radar interferogram would show elongated displacement lobes and generally closed or nested fringes associated with uplift and horizontal shortening of the hanging wall. Each full phase cycle represents ${\lambda }_r/2$ of line-of-sight displacement, where ${\lambda }_r$ is radar wavelength; equivalently $\Delta \varphi =\pm 4\pi d_{\mathrm{LOS}}/{\lambda }_r$, with sign fixed by processing convention.^[ref]

If primary slip reaches the surface, expect a displacement discontinuity across the surface trace: fringes can terminate or change abruptly there, and large near-fault gradients or disturbed ground may decorrelate. For a blind reverse fault, the elastic displacement field is continuous at the ground surface and spread over a broader zone, giving smoother gradients and fringes over the uplifted fold. A blind rupture can still create sharp local gradients or secondary faulting.

The exact colour order, number of fringes and sign of the displacement lobes cannot be fixed from this shaded relief alone. They depend on slip, depth and radar look direction; uplift is only one contribution to line-of-sight displacement.

A blind reverse fault can transfer displacement into folding above its buried tip. Look for an asymmetric growing anticline, often with a steep forelimb and gentler backlimb, aligned with the inferred fault strike. A fault-propagation fold is one possible geometry; the fold alone does not uniquely establish the fault's depth or shape. Exposed older geological strata may be more steeply tilted than younger deposits, while growth strata thin and onlap toward an uplifting crest or fan in dip as deformation accumulates. Progressive unconformities and warped young deposits help distinguish active folding from an inherited fold.

In the landscape, seek an elongate uplifted ridge, warped or tilted river terraces and alluvial fans, localized fold scarps, incision across the rising structure, and drainage deflection or abandoned channels. Compare landforms of known relative ages: increasing deformation with age records repeated motion. Opposite fold limbs may show contrasting uplift and tilting, while active axial surfaces can concentrate deformation into narrow belts even without the main fault reaching the surface. Combine geological mapping and dating with seismic reflection or evidence from geodesy where available; an erosional ridge alone is not proof of a buried active reverse fault.^[ref]