Figure 4(a)---Crustal earthquakes with magnitudes >M4.0 and depths <30 km in northern Cascadia from National Earthquake Information Center (NEIC) database. Selected fault zones indicated as in Figure 1. OWL=Olympic-Wallowa lineament of Raisz (1945). Published focal mechanisms for earthquakes larger than M6.0 in the region shown are from Hyndman et al. (1979), Baker and Langston (1987), Langston and Blum (1977), and Ludwin et al., (1992). There is no focal mechanism determination for the large 1874 earthquake in northern Washington. Contours of depth (in km) to subducting Juan de Fuca plate mantle determined from velocity modeling in this report are shown as dotted lines.