A new 3D map of the Los Angeles basin has revealed deep layers of sediment that could make earthquake shaking more intense in the region. Scientists now have a more detailed view of the ground beneath Los Angeles, showing that downtown is built on up to 6.2 miles (10 kilometers) of sediment. This layer of material can amplify the shaking caused by earthquakes, making certain areas more vulnerable. While scientists have long known that sediment can affect earthquake shaking, this new map provides a much more precise picture, helping experts better understand which parts of the city are at the highest risk. The Los Angeles basin is a large, low-lying area where layers of sediment have built up over at least 15 million years. Initially, the basin was underwater, and the earliest layers of sediment were deposited by the ocean. Later, tectonic forces raised the basin above sea level, allowing more sediment from nearby mountains to accumulate over time. Although scientists had a general idea of the basin’s shape, the new 3D map offers much greater detail, revealing the exact contours of the basin’s edges and depth of sediment. This detailed map was created using data from 273 temporary seismic stations placed around Los Angeles. These stations recorded faint earthquake waves from distant quakes that were too small to be felt by people. By analyzing how these waves traveled through the Earth, researchers were able to create a three-dimensional model of the rock layers beneath the city. The central part of the basin, under downtown Los Angeles, has the thickest sediment layer, while the edges are thinner, with only 0.6 to 2.5 miles (1 to 4 kilometers) of sediment before reaching hard, crystalline rock. While the map itself doesn’t pinpoint exactly where the most severe shaking will occur during a major earthquake, it provides critical information that can be used to improve earthquake models and simulations. The actual damage from an earthquake will depend on many factors, including which fault is involved. Los Angeles is surrounded by several faults, including the San Andreas Fault, which could generate a magnitude 7.8 earthquake. Understanding the sediment layers beneath the city can help engineers design buildings that are less likely to resonate with the shaking, reducing potential damage. By adjusting the stiffness of buildings and other structural features, engineers can mitigate the effects of resonance, ensuring structures are better prepared for the ground conditions beneath them.