Tectonic Implications of Small Earthquakes in the Central Transverse Ranges

Fault-plane solutions for 22 small (local magnitude (M_L ≤ 4.6) earthquakes in the central Transverse Ranges were determined using an azimuthally varying crustal model. The dominant type of faulting observed is reverse faulting on east-striking planes, which suggests a regional stress field characterized by north-south compression. Some strike-slip faulting also occurs. There is some indication that strike-slip earthquakes may be more common than reverse-slip earthquakes during episodes of crustal dilatation. The rate of north-south crustal shortening attributable to small-0earthquake deformation during 1974-76 is two orders of magnitude smaller than the north-south contraction of 0.3 parts per million per year measured at the surface. The scatter in earthquake hypocenters and the general inconsistency of focal mechanisms with geologically determined motions on nearby major faults indicate that the small earthquakes in this region are not associated with large-scale block movements along major fault systems. Rather, they appear to represent fracturing along random minor zones of weakness in response to the regional stress field or, alternatively, small-scale block movements that are below the resolution of this study. Earthquakes in the San Gabriel Mountains north of the Santa Susana-Sierra Madre-Cucamonga frontal fault system tend to concentrate near the eastern and western ends of the range, where good evidence for late Quaternary movement along the frontal faults has been found. Seismicity is markedly lower north of the central section of the frontal fault system, where evidence for late Quaternary movement is lacking

Waveforms and spectra of preshocks and aftershocks of the 1979 Imperial Valley, California, Earthquake: evidence for fault hetergeneity

We have compared digitally-recorded waveforms of M_L 2.0–2.8 earthquakes that occurred in two small areas along the Imperial fault before and after it broke in the ML 6.6 Imperial Valley earthquake on October 15, 1979. Eight preshocks (1977–1979) from a 4½ by 1½ km area centered 4 km SE of the mainshock epicenter have strikingly similar waveforms over the entire record length (∼30 s), with an average peak cross correlation between seismograms of 0.74. The seismograms are well correlated at frequencies up to at least 4 Hz. This implies similar source mechanisms and hypocenters within ¼ of the 4-Hz wavelengths, i.e., <200–400 m. Five aftershocks from the same area show an average peak cross correlation between seismograms of only 0.23. Any associated changes in mechanism must be small because they are not reflected in the first motion data. Analysis of frequency content of these events using bandpass-filtering techniques showed no systematic temporal changes in spectral shape. Ten preshocks and 24 aftershocks from a 1½ by 2 km source area centered along the fault 16 km NW of the mainshock epicenter were also studied. First motion data suggest that all of the aftershocks and a swarm of six preshocks on December 7–9, 1978, were associated with the main fault but that four earlier preshocks were not. The six preshocks on December 7–9, 1978, were tightly clustered, as evidenced by the strong similarity of the waveforms (most peak cross correlations ≥0.6). During this swarm the 8- to 16-Hz spectral amplitude increased relative to the 1- to 2-Hz spectral amplitude over the whole record length by about a factor of 3, suggesting a systematic increase in stress drop. Groups of like events are also present among the aftershocks in this data set. The average peak correlation for pairs of aftershocks, 0.43, is almost the same as that for pairs of preshocks, 0.45, if all 10 preshocks are included. However, several sources appear to have been active simultaneously during the aftershock period so that no more than two to three consecutive aftershocks have maximum cross correlations ≥0.6. The highly localized sources characterized by waveform similarity may represent fault asperities or clusters of asperities. Our observations are consistent with a decrease in the number of these asperities as the weaker ones fail under increasing stress during the intervals between large earthquakes

Contemporary tectonics of the Wasatch front region, Utah, from earthquake focal mechanisms

We have completed a comprehensive study of focal mechanisms of digitally recorded earthquakes (M, -_< 4.4) that occurred in the Wasatch front region in Utah during 1980 to 1986. Single-event solutions for 24 events were determined using recently revised crustal models and a computerized grid-search technique. Overall, the mechanisms show predominantly normal faulting on N-S-striking nodal planes of moderate to steep dip (>30°). Tension-axis azimuths average 96 ° _+ 12% Thus, in general, the mechanisms indicate E-W to ESE-WNW crustal extension and vertical crustal shortening. Oblique slip, when observed, is characterized by left-lateral motion on planes striking N to NE or right-lateral motion on planes striking N to NW. Most of the mechanisms with significant amounts of oblique-slip motion occur in the southern part of the study area, where compression- axis orientations range from near vertical to near horizontal. Thus, the mechanisms suggest a possible change in stress regime from north to south along the Wasatch front. Despite geologic evidence for low-angle faults in the study area, shallowly dipping nodal planes are relatively uncommon.This research was supported by the U.S. Geological Survey, Department of the Interior, under award numbers 14-08-0001-Gl163 and 14-08-0001- G1349. Partial support also came from a scholarship awarded by the Society of Exploration Geophysicists and sponsored by the Sohio Petroleum Company.Peer Reviewe

Seismicity near Palmdale, California, and its relation to strain changes

We evaluate the relationships between the spatio-temporal patterns and faulting mechanisms of small earthquakes and the recent temporal changes in horizontal strain observed along the ‘big bend’ portion of the San Andreas fault near Palmdale, California. Microearthquake activity along the entire big bend of the San Andreas fault increased in November 1976 concurrent with the initiation of an earthquake swarm at Juniper Hills. This activity then decreased abruptly to the northwest and southeast of Juniper Hills during the beginning of 1979. This drop in seismic activity occurred around the time that crustal dilatation was observed on the U. S. Geological Survey Palmdale trilateration network. Focal mechanisms from the study region are predominantly thrust. There are two time periods when the mechanisms are closer to strike slip than to thrust. The first period (December 1976 to February 1977) corresponds to the beginning of the Juniper Hills swarm. The second period (November 1978 to April 1979) approximately coincides with a change in trend of the strain data from uniaxial N-S compression to dilatation

Waveforms and spectra of preshocks and aftershocks of the 1979 Imperial Valley, California, earthquake: Evidence for fault heterogeneity?

We have compared digitally‐recorded waveforms of M_L 2.0–2.8 earthquakes that occurred in two small areas along the Imperial fault before and after it broke in the M_L 6.6 Imperial Valley earthquake on October 15, 1979. Eight preshocks (1977–1979) from a 4½ by 1½ km area centered 4 km SE of the mainshock epicenter have strikingly similar waveforms over the entire record length (∼30 s), with an average peak cross correlation between seismograms of 0.74. The seismograms are well correlated at frequencies up to at least 4 Hz. This implies similar source mechanisms and hypocenters within ¼ of the 4‐Hz wavelengths, i.e., <200–400 m. Five aftershocks from the same area show an average peak cross correlation between seismograms of only 0.23. Any associated changes in mechanism must be small because they are not reflected in the first motion data. Analysis of frequency content of these events using bandpass‐filtering techniques showed no systematic temporal changes in spectral shape. Ten preshocks and 24 aftershocks from a 1½ by 2 km source area centered along the fault 16 km NW of the mainshock epicenter were also studied. First motion data suggest that all of the aftershocks and a swarm of six preshocks on December 7–9, 1978, were associated with the main fault but that four earlier preshocks were not. The six preshocks on December 7–9, 1978, were tightly clustered, as evidenced by the strong similarity of the waveforms (most peak cross correlations ≥0.6). During this swarm the 8‐ to 16‐Hz spectral amplitude increased relative to the 1‐ to 2‐Hz spectral amplitude over the whole record length by about a factor of 3, suggesting a systematic increase in stress drop. Groups of like events are also present among the aftershocks in this data set. The average peak correlation for pairs of aftershocks, 0.43, is almost the same as that for pairs of preshocks, 0.45, if all 10 preshocks are included. However, several sources appear to have been active simultaneously during the aftershock period so that no more than two to three consecutive aftershocks have maximum cross correlations ≥0.6. The highly localized sources characterized by waveform similarity may represent fault asperities or clusters of asperities. Our observations are consistent with a decrease in the number of these asperities as the weaker ones fail under increasing stress during the intervals between large earthquakes

Efficacy of baricitinib in patients with moderate-to-severe rheumatoid arthritis up to 6.5 years of treatment: results of a long-term study

Objectives: To evaluate the long-term efficacy of once-daily baricitinib 4 mg or 2 mg in patients with active rheumatoid arthritis who had inadequate response (IR) to MTX, csDMARDs or bDMARDs. Methods: Data from three completed phase III studies—RA-BEAM (MTX-IR), RA-BUILD (csDMARD-IR) and RA-BEACON (bDMARD-IR)—and one completed long-term extension study (RA-BEYOND) were analysed up to 6.5 years [340 weeks (RA-BEAM) and 336 weeks (RA-BUILD and RA-BEACON)]. Low disease activity (LDA) [Simplified Disease Activity Index (SDAI) ≤11], clinical remission (SDAI ≤3.3) and physical function [Health Assessment Questionnaire Disability Index (HAQ-DI) ≤0.5] were the main outcomes assessed. Completer and non-responder imputation (NRI) analyses were conducted on each population. Results: At week 340 or 336, LDA was achieved in 37%/83% of MTX-IR, 35%/83% of csDMARD-IR and 23%/73% of bDMARD-IR patients treated with baricitinib 4 mg, assessed by NRI/completer analyses, respectively. Remission was achieved in 20%/40% of MTX-IR, 13%/32% of csDMARD-IR and 9%/30% of bDMARD-IR patients treated with baricitinib 4 mg, assessed by NRI/completer analyses, respectively. HAQ-DI ≤0.5 was reached in 31%/51% of MTX-IR, 25%/46% of csDMARD-IR and 24%/38% of bDMARD-IR patients treated with baricitinib 4 mg, assessed by NRI/completer analyses, respectively. Conclusion: Treatment with baricitinib 4 mg or 2 mg demonstrated efficacy up to 6.5 years with maintained LDA/remission results across SDAI, CDAI and DAS28-hsCRP consistent with previously reported data, and was well tolerated. Trial registration: United States National Library of Medicine clinical trials database www.clinicaltrials.gov; RA-BEYOND; NCT01885078

Neuroligin 1 is dynamically exchanged at postsynaptic sites

Neuroligins are postsynaptic cell adhesion molecules that associate with presynaptic neurexins. Both factors form a transsynaptic connection, mediate signaling across the synapse, specify synaptic functions, and play a role in synapse formation. Neuroligin dysfunction impairs synaptic transmission, disrupts neuronal networks, and is thought to participate in cognitive diseases. Here we report that chemical treatment designed to induce long-term potentiation or long-term depression (LTD) induces neuroligin 1/3 turnover, leading to either increased or decreased surface membrane protein levels, respectively. Despite its structural role at a crucial transsynaptic position, GFP-neuroligin 1 leaves synapses in hippocampal neurons over time with chemical LTD-induced neuroligin internalization depending on an intact microtubule cytoskeleton. Accordingly, neuroligin 1 and its binding partner postsynaptic density protein-95 (PSD-95) associate with components of the dynein motor complex and undergo retrograde cotransport with a dynein subunit. Transgenic depletion of dynein function in mice causes postsynaptic NLG1/3 and PSD-95 enrichment. In parallel, PSD lengths and spine head sizes are significantly increased, a phenotype similar to that observed upon transgenic overexpression of NLG1 (Dahlhaus et al., 2010). Moreover, application of a competitive PSD-95 peptide and neuroligin 1 C-terminal mutagenesis each specifically alter neuroligin 1 surface membrane expression and interfere with its internalization. Our data suggest the concept that synaptic plasticity regulates neuroligin turnover through active cytoskeleton transport

New On Line Resource for Psycholinguistic

Picture naming is a widely used technique in psycholinguistic studies. Here, we describe new on-line resources that our project has compiled and made available to researchers on the world wide web at http://crl.ucsd.edu/~aszekely/ipnp/. The website provides access to a wide range of picture stimuli and related norms in seven languages. Picture naming norms, including indices of name agreement and latency, for 520 black-and-white drawings of common objects and 275 concrete transitive and intransitive actions are presented. Norms for age-of-acquisition, word-frequency, familiarity, goodness-of-depiction, and visual complexity are included. An on-line database query system can be used to select a specific range of stimuli, based on parameters of interest for a wide range of studies on healthy and clinical populations, as well as studies of language development