It is proposed herein to continue sampling along the San Andreas fault in order to find more old-aged trees that have been disturbed by earthquakes. These disturbed trees can provide information about timing and extent of prehistoric earthquake events as their records of annual growth rings are dated and deciphered. Previous tree-ring ssampling and new samples from the first supported part of this project confirm the effects of the 1857 earthquake in certain trees in southern California. Samples along a 10 km length of the San Andreas fault just northwest of Cajon Pass show evidence of strong disturbance between the growing seasons of 1812 and 1813. A reported great earthquake in 1812 encourages the interpretation that tree-ring data can define the location of this earthquake, which is known in time but not in space. Further sampling and study will ensue in this area, because the interval of only 44 years, between 1812 (December) and 1857 (January), is much shorter than previous estimated recurrence intervals along this segment. Precise delineation of extent of rupture in late 1812 will be the primary focus of this research. Studies will also continue on samples from other segments of the San Andreas fault. Within constraints of time, efforts will continue in northern California. The concentration there will be on the extent of the 1838 event in the Bay Area region.
