Satellite-Based Investigations of the Transition from an Oceanic to Continental Transform Margin

Detailed characterization of neotectonics evolution of the Valle de San Felipe and Arroyo Grande regions in northern Baja California. Reoccupied GEOMEX GPS sites, and occupied a regional GPS (Global Positioning System) network. The Baja California peninsula in Mexico offers a unique setting for studying the kinematic evolution of a complex, active strike-slip/rift plate boundary. We are currently conducting remote sensing, geologic, and geodetic studies of this boundary. The combined data sets will yield instantaneous and time integrated views of its evolution. This proposal solicits renewed funding from NASA to support remote sensing and geologic studies. During the late Cenozoic, Baja California has been the locus of changing fault geometry that has accommodated components of the relative motion between the North America and Pacific plates. Contemporary slip between the two plates occurs in a broad zone that encompasses much of southern California and the Baja California Peninsula. The transfer of slip across this zone in southern California is relatively well understood. South of the border, the geometry and role of specific faults and structural provinces in transferring plate margin deformation across the peninsula is enigmatic. Results We use Landsat Thematic Mapper imagery of the Baja California Peninsula to identify recent and active faults, and then conduct field studies that characterize the temporal and spatial structural evolution of the plate margin. These data address questions concerning the neotectonic development of the Gulf of California, the Baja California Peninsula, and their role in evolution of the post-Miocene Pacific - North American plate boundary. Moreover, these studies provide constraints on the geometry of active faults, allowing more exact understanding of the results of ongoing NASA-supported geodetic experiments. In addition, anticipated publication of the TM scenes will provide a widely available geological data base for relatively little-known peninsula California. Achievements include development of an ArcInfo data base of Landsat and SPOT imagery, detailed field studies of Neogene structures in northeastern Baja California, and new constraint on Pacific - North America plate motion at Baja California latitudes. These results are reported in maps, manuscripts and data products which are published or near completion

GPS Monitoring of Surface Change During and Following the Fortuitous Occurrence of the M(sub w) = 7.3 Landers Earthquake in our Network

Accomplishments: (1) Continues GPS monitoring of surface change during and following the fortuitous occurrence of the M(sub w) = 7.3 Landers earthquake in our network, in order to characterize earthquake dynamics and accelerated activity of related faults as far as 100's of kilometers along strike. (2) Integrates the geodetic constraints into consistent kinematic descriptions of the deformation field that can in turn be used to characterize the processes that drive geodynamics, including seismic cycle dynamics. In 1991, we installed and occupied a high precision GPS geodetic network to measure transform-related deformation that is partitioned from the Pacific - North America plate boundary northeastward through the Mojave Desert, via the Eastern California shear zone to the Walker Lane. The onset of the M(sub w) = 7.3 June 28, 1992, Landers, California, earthquake sequence within this network poses unique opportunities for continued monitoring of regional surface deformation related to the culmination of a major seismic cycle, characterization of the dynamic behavior of continental lithosphere during the seismic sequence, and post-seismic transient deformation. During the last year, we have reprocessed all three previous epochs for which JPL fiducial free point positioning products available and are queued for the remaining needed products, completed two field campaigns monitoring approx. 20 sites (October 1995 and September 1996), begun modeling by development of a finite element mesh based on network station locations, and developed manuscripts dealing with both the Landers-related transient deformation at the latitude of Lone Pine and the velocity field of the whole experiment. We are currently deploying a 1997 observation campaign (June 1997). We use GPS geodetic studies to characterize deformation in the Mojave Desert region and related structural domains to the north, and geophysical modeling of lithospheric behavior. The modeling is constrained by our existing and continued GPS measurements, which will provide much needed data on far-field strain accumulation across the region and on the deformational response of continental lithosphere during and following a large earthquake, forming the basis for kinematic and dynamic modeling of secular and seismic-cycle deformation. GPS geodesy affords both regional coverage and high precision that uniquely bear on these problems

Permian and Triassic Paleogeography of the Eastern Klamath Arc and Eastern Hayfork Subduction Complex, Klamath Mountains, California: Evidence from Lithotectonic Associations and Detrital Zircon

Middle Permian and Middle Triassic volcanic-hypabyssal intrusive complexes form ensimatic arc deposits in the eastern Klamath terrane. Sedimentary matrix melange with blocks of sandstone, chert, and Tethyan fauna-bearing limestone compose the westward-lying eastern Hayfork terrane. Limestone olistoliths were derived from seamounts and incorporated into a subduction complex that was active during the Late Triassic and perhaps as early as the Permian. Geologic and biogeographic relations have previously been interpreted to imply a genetic relation between an ensimatic arc and subduction complex, constraining Permian(?)-Triassic subduction as eastward dipping

U-Pb geochronology of detrital zircon from Upper Jurassic synorogenic turbidites, Galice Formation, and related rocks, western Klamath Mountains: Correlation and Klamath Mountains provenance

Synorogenic turbidites of the Upper Jurassic Galice Formation overlie a variety of basement terranes within the western Klamath Mountains along the Oregon-California border, including the early Late Jurassic ophiolite assemblages, ensimatic arc deposits, and sedimentary terranes. U-Pb analyses of 68 multiple grain fractions from 11 samples of detrital zircon support the correlation of Galice Formation on these various basement terranes, although some new complexities in provenance are revealed. With one exception, upper intercept ages range from 1509^(+3)_(-3) to 1675^(+8)_(-8) Ma. Least squares regression of all fractions yields an upper intercept age of 1583±1 Ma, indicating the importance of an ultimately continental, recycled, and generally well-mixed sedimentary source. Early Mesozoic lower intercept ages range between 183^(+2)_(-2) and 263^(+4)_(-3) and average 215±1 Ma. Results from Galice cover on sedimentary basement show significantly older 2.1 Ga Precambrian component, however, that may be locally derived from pre-Late Jurassic basement rocks that are rich in recycled sedimentary debris. Existing isotopic data from older, zircon-bearing Klamath units further indicate that Galice detritus was derived from immediate source terranes within the Klamath Mountains. Reworking of fragile limestone clasts from the biogeographically distinctive eastern Klamath terrane (McCloud Limestone) into Galice Formation substrate also supports early paleogeographic ties between terranes. Thus the tectonic setting of the Late Jurassic Nevadan orogeny in the Klamath Mountains is tightly constrained by original paleogeographic ties between subterranes of the western belt and by provenance ties to terranes to the east. Ultimately continent-derived clastic debris and other distinctive tracers were recycled within this long-lived ensimatic convergent margin system

Refined kinematics of the Eastern California shear zone from GPS observations, 1993-1998

Global Positioning System (GPS) results from networks spanning the Eastern California shear zone and adjacent Sierra Nevada block, occupied annually between 1993 and 1998, constrain plate margin kinematics. We use an elastic block model to relate GPS station velocities to long‐term fault slip rate estimates. The model accounts for elastic strain accumulation on the San Andreas fault, as well as faults of the Eastern California shear zone. South of the Garlock fault, 14 mm/yr of dextral shear is distributed across the Eastern California shear zone. Some of this slip penetrates eastward into the Basin and Range, and a collective budget of 13 mm/yr is observed to the north at the latitude of Owens Lake. Model slip rates for two important faults, the Garlock and Owens Valley faults, significantly misfit geologic estimates. By referencing station velocities to stable North America we observe northward‐increasing deformation east of our regional GPS network. At the latitude of Mojave Desert, however, some of this deformation is ascribed to elastic strain accumulation due to a locked San Andreas fault and thus does not represent additional fault‐related, permanent deformation

Major disruption of D″ beneath Alaska

D″ represents one of the most dramatic thermal and compositional layers within our planet. In particular, global tomographic models display relatively fast patches at the base of the mantle along the circum-Pacific which are generally attributed to slab debris. Such distinct patches interact with the bridgmanite (Br) to post-bridgmanite (PBr) phase boundary to generate particularly strong heterogeneity at their edges. Most seismic observations for the D″ come from the lower mantle S wave triplication (Scd). Here we exploit the USArray waveform data to examine one of these sharp transitions in structure beneath Alaska. From west to east beneath Alaska, we observed three different characteristics in D″: (1) the western region with a strong Scd, requiring a sharp δVs = 2.5% increase; (2) the middle region with no clear Scd phases, indicating a lack of D″ (or thin Br-PBr layer); and (3) the eastern region with strong Scd phase, requiring a gradient increase in δVs. To explain such strong lateral variation in the velocity structure, chemical variations must be involved. We suggest that the western region represents relatively normal mantle. In contrast, the eastern region is influenced by a relic slab that has subducted down to the lowermost mantle. In the middle region, we infer an upwelling structure that disrupts the Br-PBr phase boundary. Such an interpretation is based upon a distinct pattern of travel time delays, waveform distortions, and amplitude patterns that reveal a circular-shaped anomaly about 5° across which can be modeled synthetically as a plume-like structure rising about 400 km high with a shear velocity reduction of ~5%, similar to geodynamic modeling predictions of upwellings

Southern Cascadia Episodic Slow Earthquakes

Continuous GPS and seismic data from northern California show that slow earthquakes periodically rupture the Gorda-North America plate interface within southern Cascadia. On average, these creep events have occurred every 10.9±1.2 months since at least 1998. Appearing as week-long GPS extensional transients that reverse secular forearc contraction, the data show a recurrence interval 22% shorter than slow events recognized to the north. Seismic tremor here accompanies the GPS reversals, correlated across as many as 5 northern California seismometers. Tremor occurs sporadically throughout the year, but increases in duration and intensity by a factor of about 10 simultaneous with the GPS reversals. Beneath west-central Oregon, three reversals are also apparent, but more stations are needed to confirm sporadic slip on the plate interface here. Together, these measurements suggest that slow earthquakes likely occur throughout the Cascadia subduction zone and add further evidence for the role of fault-fluid migration in controlling transient slow-slip events here

Southern Cascadia episodic slow earthquakes

Continuous GPS and seismic data from northern California show that slow earthquakes periodically rupture the Gorda‐North America plate interface within southern Cascadia. On average, these creep events have occurred every 10.9 ± 1.2 months since at least 1998. Appearing as week‐long GPS extensional transients that reverse secular forearc contraction, the data show a recurrence interval 22% shorter than slow events recognized to the north. Seismic tremor here accompanies the GPS reversals, correlated across as many as 5 northern California seismometers. Tremor occurs sporadically throughout the year, but increases in duration and intensity by a factor of about 10 simultaneous with the GPS reversals. Beneath west‐central Oregon, three reversals are also apparent, but more stations are needed to confirm sporadic slip on the plate interface here. Together, these measurements suggest that slow earthquakes likely occur throughout the Cascadia subduction zone and add further evidence for the role of fault‐fluid migration in controlling transient slow‐slip events here

Utility of the Language Use Inventory in Young Children at Elevated Likelihood of Autism

PurposeThe aims of this study were (a) to evaluate the convergent validity of the Language Use Inventory (LUI) with measures of autism spectrum disorder (ASD) symptoms, language, and social skills and (b) to assess discriminant validity of the LUI with measures of nonlanguage skills, including daily living skills and motor development.MethodThis study sample included participants from a longitudinal study (n = 239) of infant siblings with elevated familial likelihood of ASD and lower familial likelihood. Assessment measures completed at 36 months included the LUI, the Autism Diagnostic Observation Schedule-Second Edition (ADOS-2), the Mullen Scales of Early Learning, and the Vineland Adaptive Behavior Scales-Second Edition. Bivariate Pearson correlations were estimated between ADOS-2 comparison scores and four language and social skills measures. Additional correlations were estimated between LUI total scores and standard scores from nonlanguage measures. A series of Fisher's Z transformations were applied to evaluate whether bivariate correlations were significantly different.ResultsAll four language and social skill measures were moderately to strongly associated with each other and ASD symptom severity scores. The correlation between ADOS-2 comparison scores and LUI total scores was significantly stronger than ADOS-2 correlations with all other measures.ConclusionsOur findings provide support for the LUI as a feasible, pragmatic language-targeted instrument for inclusion in early developmental evaluations prompted by language concerns. Administration of the LUI may accelerate earlier referral for a comprehensive assessment of ASD symptoms. Given the high correlation with ADOS-2 scores, an LUI total score in a clinical range of concern may encourage a clinician to refer families for a full diagnostic evaluation of ASD

Dyadic Synchrony and Responsiveness in the First Year: Associations with Autism Risk

In the first year of life, the ability to engage in sustained synchronous interactions develops as infants learn to match social partner behaviors and sequentially regulate their behaviors in response to others. Difficulties developing competence in these early social building blocks can impact later language skills, joint attention, and emotion regulation. For children at elevated risk for autism spectrum disorder (ASD), early dyadic synchrony and responsiveness difficulties may be indicative of emerging ASD and/or developmental concerns. As part of a prospective developmental monitoring study, infant siblings of children with ASD (high-risk group n = 104) or typical development (low-risk group n = 71), and their mothers completed a standardized play task when infants were 6, 9, and/or 12 months of age. These interactions were coded for the frequency and duration of infant and mother gaze, positive affect, and vocalizations, respectively. Using these codes, theory-driven composites were created to index dyadic synchrony and infant/maternal responsiveness. Multilevel models revealed significant risk group differences in dyadic synchrony and infant responsiveness by 12 months of age. In addition, high-risk infants with higher dyadic synchrony and infant responsiveness at 12 months received significantly higher receptive and expressive language scores at 36 months. The findings of the present study highlight that promoting dyadic synchrony and responsiveness may aid in advancing optimal development in children at elevated risk for autism. Lay Summary: In families raising children with an autism spectrum disorder (ASD), younger siblings are at elevated risks for social communication difficulties. The present study explored whether social-communication differences were evident during a parent–child play task at 6, 9, and 12 months of age. For infant siblings of children with ASD, social differences during play were observed by 12 months of age and may inform ongoing monitoring and intervention efforts