THE EMERSON LAKE BODY: A DENSE, MAGNETIC KNOT WITHIN THE EASTERN CALIFORNIA SHEAR ZONE
Seismicity before the Landers earthquake also tended to avoid the ELB, suggesting that the ELB affects the distribution of stress in this part of the Mojave Desert. Even though the 1975 Galway Lake earthquakes (M5.4) overlap the subsurface extent of the body in plan view, the earthquakes were shallow (< 5 km) and tended to occur above the ELB. The 1979 Homestead Valley earthquakes (M5.3) were also shallow, occurring along a set of conjugate faults. The Homestead Valley aftershocks occurred within an embayment in the western margin of the ELB.
Because the ELB is older than the Miocene initiation of movement on the eastern California shear zone, we predict less cumulative offset on faults within the body than on faults outside the body. Analysis of high-resolution aeromagnetic data does not indicate measurable apparent right-lateral offset (> 1 km) on faults within the ELB, but does find higher cumulative offset (3-20 km) on faults outside the ELB. Detailed gravity indicates an east-striking stream channel that crosses the Hidalgo fault without any right-lateral deflection. Thus, the ELB influences the way strain is accommodated throughout this part of the Mojave Desert.