FA-71487 / Seismic magnitude estimation / Member archive

Coda duration magnitude: duration log base · case 02

Md grows too fast with duration.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

envelope is a list of amplitude samples, dt s per sample, p_index the P pick sample, noise the pre-event noise level. From the peak at or after the pick (first maximum), the coda ends at the first sample with amplitude <= 2*noise. tau = (end - p_index)*dt; Md = -0.87 + 2.0 log10(tau) + 0.0035 epi_km. Return [tau rounded 0.01, Md rounded 0.01] or None when no end or tau <= 0.

Why this case matters

Duration magnitude is robust for small events with clipped or noisy amplitudes.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
coda 3	`[4.0, 1.92]`	`[4.0, 0.35]`	Failed

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