The Effect of the 1857 Fort Tejon Earthquake on Trees near Wrightwood, California

Trees may suffer damage during major earthquakes due to shaking and faulting of the ground beneath them. External effects, such as topping, root and limb damage, and scars may result in a temporary reduction in the width of their annual growth rings. Tilting and changes in environmental factors, such as light, space and water availability may initiate asymmetric growth. Dendrochronologic techniques enable dating of such growth anomalies, and hence earthquakes

The Effect of the 1857 Fort Tejon Earthquake on Trees near Wrightwood, California

Trees may suffer damage during major earthquakes due to shaking and faulting of the ground beneath them. External effects, such as topping, root and limb damage, and scars may result in a temporary reduction in the width of their annual growth rings. Tilting and changes in environmental factors, such as light, space and water availability may initiate asymmetric growth. Dendrochronologic techniques enable dating of such growth anomalies, and hence earthquakes

Disturbance of trees by the 1857 Fort Tejon earthquake, California

Trees may suffer damage during major earthquakes due to shaking or faulting of their substrate. Damage may result in temporarily asymmetric growth and/or reduction in width of annual growth rings. To determine whether trees contain useful records of prehistoric earthquakes in southern California, we cored eight conifers along the 1857 trace of the San Andreas fault near Wrightwood and Frazier Park, California. Annual ring widths were measured and plotted against the growth year determined by ring counting.We examined significant departures from normal growth trends and interpreted them in light of the 1857 earthquake and other possible environmental factors. Of eight trees sampled, five showed damage or growth anomalies attributablet o the 1857 event. One 120-year-old t ree straddling the fault is undamaged, suggesting no substantial slip since about 1870. To evaluate asymmetry, ratios of correlative rings widths from opposite sides of three seismically damaged trees were calculated and plotted against growth year. Two types of ratio anomalies can be recognized:(1) short-term,unilateral suppression of growth resulting from damage and (2) long-term,unilateral enhancement of growth attributable to tilt or changes in environmental factors. Further study of ring ratio anomalies may facilitate recognition of seismically damaged trees. Success in recognizing the 1857 event in five out of eight trees suggests that a larger suite of even older trees may contain a valuable 'dendroseismological' record of large prehistoric earthquakes in southern California.Published versio

First bedrock samples dredged from submarine outcrops in the Chukchi Borderland, Arctic Ocean

The Chukchi Borderland, a prominent bathymetric feature within the Arctic Ocean, has been interpreted as a fragment of an undeformed continental platform sequence rifted from the passive margin of Arctic Canada. Dredges collected for the U.S. Extended Continental Shelf project aboard the icebreaker U.S. Coast Guard Cutter Healy (cruise number HLY0905) recovered hundreds of kilograms of broken crystalline basement lithologies consisting of mylonitically deformed biotite-bearing amphibolite, garnet-bearing feldspathic gneiss, and augen-bearing orthogneiss from the Chukchi Borderland. Metamorphic zircon within the amphibolite and associated leucogranitic seams within these rocks yielded U-Pb zircon ages between ca. 480 and 530 Ma. Garnet-bearing feldspathic gneisses contain variably discordant Mesoproterozoic zircon, ca. 600 Ma igneous zircon, and ca. 485–505 Ma metamorphic overgrowths. While we interpret these gneisses as deformed and metamorphosed granitoids, they could, instead, have a very immature sedimentary protolith. The youngest rocks sampled were K-feldspar augen orthogneisses that yield ca. 430 Ma zircon crystallization ages. Whole-rock geochemistry and Sr-Nd isotopic data indicate that the orthogneisses are I-type calc-alkaline granitoids. All of the basement rocks including the orthogneisses are variably metamorphosed and mylonitized. Collectively, the U-Pb age, geochemistry, and fabric of the dredged Chukchi Borderland basement samples indicate that they represent Neoproterozoic–Ordovician orogenic crust and Silurian arc batholithic rocks. This geologic origin is inconsistent with the Neoproterozoic to early Paleozoic passive margin history of western Arctic Canada to which the Chukchi Borderland has been previously correlated. We alternatively propose that the basement of the Chukchi Borderland is related to the peri-Laurentian composite terranes of Pearya and western Svalbard that have similar geologic histories

Circum-Arctic Lithosphere Evolution (CALE) Transect C: displacement of the Arctic Alaska–Chukotka microplate towards the Pacific during opening of the Amerasia Basin of the Arctic

Supplementary material Plate 1 comprises Plate 1 and its included figures. Plate 1 contains regional reflection-seismic-based cross sections and supporting material that collectively constitute CALE Transects C1 and C2. Plate 1 is referred to in the text as Sup. Pl. 1, Transects C1 and C2 as Plate 1A and 1B, and plate figures as fig. P1.1, fig. P1.2, etc.)