Modeling of ground motion from a 1994 Northridge aftershock using a tomographic velocity model of the Los Angeles Basin

The 1994 Northridge mainshock and its aftershocks show a complex pattern of peak accelerations at stations located in the Los Angeles Basin. The waveforms contain multiples of body-wave phases and extensive surface waves at frequencies mostly below 1 Hz. In particular, for stations at distances greater than 18 km, secondary arrivals show larger accelerations than the direct S-wave arrivals. The mainshock waveforms are further complicated by irregularities of the source rupture. We use 2D finite difference to evaluate the effect of lateral variations in seismic velocity on the amplitude of shear-wave energy and to distinguish the effects of source and propagation path. We model waveforms from one aftershock recorded at nine stations deployed along a 60-km-long profile extending into the Los Angeles Basin. We use a two-dimensional slice through the 3D tomography model of the Los Angeles Basin in the 2D finite-difference calculations. These synthetic waveforms fit the aftershock waveforms significantly better than corresponding waveforms determined from simple 1D velocity models. With the addition of a thin low-velocity surface layer above the tomography model, the finite-difference synthetics reproduce most of the important features of the recorded data, in particular, the large-amplitude arrivals 7 to 10 sec following the direct S arrival. These arrivals correspond to the SS arrival, which is sharply refracted at the basin edge, and the S-wave with multiple legs trapped by the dipping near surface gradient. For large earthquakes located either inside or outside the basin, these phases can be the cause of the largest and hence potentially most hazardous shaking in the Los Angeles Basin

Global Positioning System Resurvey of Southern California Seismic Network Stations

Systematic errors in travel-time data from local earthquakes can sometimes be traced to inaccuracies in the published seismic station coordinates. This prompted a resurvey of the stations of the Caltech/USGS Southern California Seismic Network (SCSN) using the Global Positioning System (GPS). We surveyed 241 stations of the SCSN using Trimble and Ashtech dual-frequency GPS receivers and calculated positions accurate to 3 m using differential positioning from carrier phase measurements. Twelve percent of the stations that were surveyed were found to be mislocated by more than 500 m. Stations of the TERRAscope and USC networks were also surveyed, as well as a network of portable seismic stations deployed shortly after the 1992 Joshua Tree and Landers earthquakes. The new coordinates and the offsets from the old coordinates are given below. The new coordinates are being used in SCSN locations as of 1 January 1994

Three-dimensional V_P and V_P/V_S Velocity Models of the Los Angeles basin and central Transverse Ranges, California

We use P and S arrival times from 5225 earthquakes and 53 explosions, recorded by the Southern California Seismographic Network, to invert for the three-dimensional P- velocity (V_P) and the P and S-velocity ratio (V_P/ V_S) in the central Transverse Ranges and the Los Angeles basin. To model long-wavelength features of the velocity structure, we invert for the models by interpolating models determined successively from a sparse, medium, to a dense grid, with 40, 20, and 10 km spacing of horizontal grid nodes. Layers of grid nodes are placed at depths of 1, 4, 6, 8, 12, 16, and 20 km. The data variance decreased about 80% in the gradational inversion. Ample data from the 1994 Northridge and other earthquake sequences, the rich background seismicity, and the dense station distribution along with controlled sources made the model well resolved, except along the edges, to the southwest in the offshore region, and at depths greater than 20 km. The V_P model images the shape of the Los Angeles and east Ventura basins down to depths of 8 and 12 km. Three low-velocity areas at 1 km depth in the Los Angeles basin that coincide with recent sediment depositional areas are also imaged. The north edge of the Peninsular Ranges, the Santa Monica, and the San Gabriel Mountains, form discontinuous high-velocity ridges extending to depths of 20 km. The high V_P/V_S ratios in the near surface are consistent with high pore fluid pressures in the basin sediments. At depth beneath the east Ventura basin the high V_P/V_S and high V_P suggest the presence of ophiolitic assemblages or mid-Miocene volcanics. In contrast, a body with normal V_P and low V_P/V_S that is identified in the upper crust beneath Santa Monica Bay may be a fragment of quartz-rich continental crust. The V_P model of both the Ventura and the Los Angeles basins shows features that suggest deformation of the hanging wall or basin closure. At seismogenic depths of 16 km the hypocenters of moderate-sized and large earthquakes are located within or adjacent to high-V_P-velocity bodies. In most cases these high-velocity bodies form the upper block, consistent with shortening of the lower crust as described in thick-skinned tectonic interpretations

Application of Reflected Global Navigation Satellite System (GNSS-R) Signals in the Estimation of Sea Roughness Effects in Microwave Radiometry

In February-March 2009 NASA JPL conducted an airborne field campaign using the Passive Active L-band System (PALS) and the Ku-band Polarimetric Scatterometer (PolSCAT) collecting measurements of brightness temperature and near surface wind speeds. Flights were conducted over a region of expected high-speed winds in the Atlantic Ocean, for the purposes of algorithm development for salinity retrievals. Wind speeds encountered were in the range of 5 to 25 m/s during the two weeks deployment. The NASA-Langley GPS delay-mapping receiver (DMR) was also flown to collect GPS signals reflected from the ocean surface and generate post-correlation power vs. delay measurements. This data was used to estimate ocean surface roughness and a strong correlation with brightness temperature was found. Initial results suggest that reflected GPS signals, using small low-power instruments, will provide an additional source of data for correcting brightness temperature measurements for the purpose of sea surface salinity retrievals

On the existence of the logarithmic surface layer in the inner-core of hurricanes

Q. J. R. Meteorol. Soc., 1394128

Specific Gene Expression Responses to Parasite Genotypes Reveal Redundancy of Innate Immunity in Vertebrates

Vertebrate innate immunity is the first line of defense against an invading pathogen and has long been assumed to be largely unspecific with respect to parasite/pathogen species. However, recent phenotypic evidence suggests that immunogenetic variation, i.e. allelic variability in genes associated with the immune system, results in host-parasite genotype-by-genotype interactions and thus specific innate immune responses. Immunogenetic variation is common in all vertebrate taxa and this reflects an effective immunological function in complex environments. However, the underlying variability in host gene expression patterns as response of innate immunity to within-species genetic diversity of macroparasites in vertebrates is unknown. We hypothesized that intra-specific variation among parasite genotypes must be reflected in host gene expression patterns. Here we used high-throughput RNA-sequencing to examine the effect of parasite genotypes on gene expression patterns of a vertebrate host, the three-spined stickleback (Gasterosteus aculeatus). By infecting naïve fish with distinct trematode genotypes of the species Diplostomum pseudospathaceum we show that gene activity of innate immunity in three-spined sticklebacks depended on the identity of an infecting macroparasite genotype. In addition to a suite of genes indicative for a general response against the trematode we also find parasite-strain specific gene expression, in particular in the complement system genes, despite similar infection rates of single clone treatments. The observed discrepancy between infection rates and gene expression indicates the presence of alternative pathways which execute similar functions. This suggests that the innate immune system can induce redundant responses specific to parasite genotypes

Within- and between-person and group variance in behavior and beliefs in cross-cultural longitudinal data

This study grapples with what it means to be part of a cultural group, from a statistical modeling perspective. The method we present compares within- and between-cultural group variability, in behaviors in families. We demonstrate the method using a cross-cultural study of adolescent development and parenting, involving three biennial waves of longitudinal data from 1296 eight-year-olds and their parents (multiple cultures in nine countries). Family members completed surveys about parental negativity and positivity, child academic and social-emotional adjustment, and attitudes about parenting and adolescent behavior. Variance estimates were computed at the cultural group, person, and within-person level using multilevel models. Of the longitudinally consistent variance, most was within and not between cultural groups—although there was a wide range of between-group differences. This approach to quantifying cultural group variability may prove valuable when applied to quantitative studies of acculturation