Microearthquake activity adjacent to the Rocklin pluton near Auburn, California

The occurrence of the Oroville earthquake (M_L = 5.7) of August 1, 1975 heightened interest in the seismotectonics of the Sierra foothills region and particularly the Foothills fault system. Clark (1960) recognized the Foothills fault system as being a major structural feature of the western Sierra Nevada. An 11-week reconnalssance microearthquake study was conducted by Woodward-Clyde Consultants (WCC) for the U.S. Bureau of Reclamation (USBR) to assess the seismic activity of the Sierra foothills 75 km S-SE of Oroville near Auburn, California. Microearthquake activity was detected in the Rocklin-Auburn region with eight events recorded during July 1 to July 24 and seven events during August 15 to October 8, 1976 (see Figure 1). The mobile seismic array consisted of eight Sprengnether MEQ-800 portable seismographs with Mark Products L-4C vertical seismometers. Data recordings were normally 48 hours in length, with a record speed of 1 mm/sec

Satellite observations for detecting and forecasting sea-ice conditions: A summary of advances made in the SPICES Project by the EU's Horizon 2020 Programme

The detection, monitoring, and forecasting of sea-ice conditions, including their extremes, is very important for ship navigation and offshore activities, and for monitoring of sea-ice processes and trends. We summarize here recent advances in the monitoring of sea-ice conditions and their extremes from satellite data as well as the development of sea-ice seasonal forecasting capabilities. Our results are the outcome of the three-year (2015-2018) SPICES (Space-borne Observations for Detecting and Forecasting Sea-Ice Cover Extremes) project funded by the EU's Horizon 2020 programme. New SPICES sea-ice products include pancake ice thickness and degree of ice ridging based on synthetic aperture radar imagery, Arctic sea-ice volume and export derived from multisensor satellite data, and melt pond fraction and sea-ice concentration using Soil Moisture and Ocean Salinity (SMOS) radiometer data. Forecasts of July sea-ice conditions from initial conditions in May showed substantial improvement in some Arctic regions after adding sea-ice thickness (SIT) data to the model initialization. The SIT initialization also improved seasonal forecasts for years with extremely low summer sea-ice extent. New SPICES sea-ice products have a demonstrable level of maturity, and with a reasonable amount of further work they can be integrated into various operational sea-ice services

Upper Crustal Structure from the Santa Monica Mountains to the Sierra Nevada, Southern California: Tomographic Results from the Los Angeles Regional Seismic Experiment, Phase II (LARSE II)

In 1999, the U.S. Geological Survey and the Southern California Earthquake Center (SCEC) collected refraction and low-fold reflection data along a 150-km-long corridor extending from the Santa Monica Mountains northward to the Sierra Nevada. This profile was part of the second phase of the Los Angeles Region Seismic Experiment (LARSE II). Chief imaging targets included sedimentary basins beneath the San Fernando and Santa Clarita Valleys and the deep structure of major faults along the transect, including causative faults for the 1971 M 6.7 San Fernando and 1994 M 6.7 Northridge earthquakes, the San Gabriel Fault, and the San Andreas Fault. Tomographic modeling of first arrivals using the methods of Hole (1992) and Lutter et al. (1999) produces velocity models that are similar to each other and are well resolved to depths of 5-7.5 km. These models, together with oil-test well data and independent forward modeling of LARSE II refraction data, suggest that regions of relatively low velocity and high velocity gradient in the San Fernando Valley and the northern Santa Clarita Valley (north of the San Gabriel Fault) correspond to Cenozoic sedimentary basin fill and reach maximum depths along the profile of ∼4.3 km and >3 km, respectively. The Antelope Valley, within the western Mojave Desert, is also underlain by low-velocity, high-gradient sedimentary fill to an interpreted maximum depth of ∼2.4 km. Below depths of ∼2 km, velocities of basement rocks in the Santa Monica Mountains and the central Transverse Ranges vary between 5.5 and 6.0 km/sec, but in the Mojave Desert, basement rocks vary in velocity between 5.25 and 6.25 km/sec. The San Andreas Fault separates differing velocity structures of the central Transverse Ranges and Mojave Desert. A weak low-velocity zone is centered approximately on the north-dipping aftershock zone of the 1971 San Fernando earthquake and possibly along the deep projection of the San Gabriel Fault. Modeling of gravity data, using densities inferred from the velocity model, indicates that different velocity-density relationships hold for both sedimentary and basement rocks as one crosses the San Andreas Fault. The LARSE II velocity model can now be used to improve the SCEC Community Velocity Model, which is used to calculate seismic amplitudes for large scenario earthquakes

A new technique to measure spatial relationships within groups of free-ranging coastal cetaceans

1. The development and calibration of a land-based technique to measure inter-animal spacing in free-ranging coastal cetaceans is described here. The technique was developed to study the behaviour of killer whales Orcinus orca in Norway.2. A theodolite was used to measure the surfacing location of one reference individual while simultaneous video recordings of the whole group were made. Digitized video frames were then used to estimate the locations of all individuals in the video frame relative to the reference animal.3. The technique was calibrated using a line of towed buoys with known separations. Estimated inter-buoy distances were compared with actual values to calculate errors. There was no observable bias in measurements, with a mean error of -0.014 m (n = 304, SD = 0.880). At ranges up to 2 km from the observation site, 95% of measurements were accurate to within 1.7 m.4. The accuracy of the measurement system was characterized with a set of Monte Carlo simulations. Simulations were run at offshore ranges from 100 m to 2000 m, with random perturbations applied to all variables. Errors in inter-animal distances for n = 16 whales were estimated using 10 000 simulation runs for every range value. The results from the simulations agreed with experimental findings. The results showed no bias in inter-animal distance measurements, with an overall mean error of 0.0864 m.5. The results indicate that this technique is suitable for studies on a variety of coastal cetacean populations. It provides a new tool for quantitative studies on spatial behaviour of cetaceans, and will help underpin management efforts to monitor effects of anthropogenic disturbance. With modification, the technique might also be applicable to other coastal vertebrates where inter-organism distances are required.</p