SHERMAN ISLAND – The earth rippled and squirmed on this Delta island Monday. It did not yawn open, but did reignite debate about the seismic safety of levees in the Sacramento-San Joaquin Delta. 

Various pictures of the Delta...Various maps of the Delta...

In the first experiment of its kind, UCLA scientists erected a shaking machine atop a model levee about the size of a two-car garage. Their goal: find out if the peat soil on Sherman Island would rupture, causing the "levee" to fail.

Peat, a spongy material composed of decaying plants rather than mineral soil, is known as a poor thing to build on. Yet it lies under most of the Sacramento-San Joaquin Delta, including its 1,100 miles of levees.

A debate has raged for years about whether those levees and their peat foundations will liquefy in a quake, potentially causing a monumental flood.