Earthquake shaking lasts only seconds, so how can it leave rock easier for later rivers to erode?

Answer: Persistent microcracks

Persistent microcracks ✓ — Right. The shaking is brief, but it can leave microfractures and weakened grain contacts in near-surface rock. That matters because rivers, landslides, and chemical weathering attack weaknesses that already exist. The event is quick; the important trace is the damaged fabric that later erosion can exploit.

Instant slope steepening — Not quite. Some earthquakes do create scarps or landslides, but that is not the durable mechanism behind this pattern. The key is rock weakening: fractures and grain contacts change the strength of the material. A steeper slope helps water move faster, but weakened rock explains why the same forcing cuts more efficiently.

Short-lived loose soil — This catches only the shallowest effect. Loose soil can wash away quickly after shaking, but the lasting effect concerns bedrock erosion across river basins. The longer-lived payoff is inside the rock fabric itself: small cracks and weakened contacts give later rivers and weathering reactions easier starting points.