I've just discussed this with @grok :

The Tartus explosion on December 15, 2024, is best characterized as a surface detonation, based on the 41 ft crater radius, the abrupt P-wave onset in the seismogram, and Braun’s analysis. A 0.3 kt surface detonation would produce significant local fallout, with some secondary activation of the surface soil, leading to a 6,000 nSv/h reading four months later, primarily from longer-lived fission products like cesium-137. The high radiation reading, combined with the implausibility of alternative sources like a chemical factory or medical devices, strengthens the case for a nuclear event, though the lack of independent verification (e.g., by the IAEA) and isotopic analysis leaves the claim unconfirmed. The evidence points to a surface burst as the most likely explanation for the observed effects.