Gravity survey of the Mt. Toondina impact structure, South Australia

The Mt. Toondina impact structure is located in northern South Australia, about 45 km south of the town of Oodnadatta. Only the central uplift is exposed. The outcrops at Mt. Toondina reveal a remarkable structural anomaly surrounded by a broad expanse of nearly flat-lying beds of the Bulldog Shale of Early Cretaceous age. A gravity survey was undertaken in 1989 to determine the diameter of the impact structure, define the form of the central uplift, and understand the local crustal structure. Data were collected along two orthogonal lines across the structure. In addition to the profiles, a significant number of measurements were made on and around the central uplift. The 1989 gravity data combined with 1963 gravity data and the seismic reflection data provide an excellent data base to interpret the subsurface structure of the Mt. Toondina feature

Precession during merger 1: Strong polarization changes are observationally accessible features of strong-field gravity during binary black hole merger

The short gravitational wave signal from the merger of compact binaries encodes a surprising amount of information about the strong-field dynamics of merger into frequencies accessible to ground-based interferometers. In this paper we describe a previously-unknown "precession" of the peak emission direction with time, both before and after the merger, about the total angular momentum direction. We demonstrate the gravitational wave polarization encodes the orientation of this direction to the line of sight. We argue the effects of polarization can be estimated nonparametrically, directly from the gravitational wave signal as seen along one line of sight, as a slowly-varying feature on top of a rapidly-varying carrier. After merger, our results can be interpreted as a coherent excitation of quasinormal modes of different angular orders, a superposition which naturally "precesses" and modulates the line-of-sight amplitude. Recent analytic calculations have arrived at a similar geometric interpretation. We suspect the line-of-sight polarization content will be a convenient observable with which to define new high-precision tests of general relativity using gravitational waves. Additionally, as the nonlinear merger process seeds the initial coherent perturbation, we speculate the amplitude of this effect provides a new probe of the strong-field dynamics during merger. To demonstrate the ubiquity of the effects we describe, we summarize the post-merger evolution of 104 generic precessing binary mergers. Finally, we provide estimates for the detectable impacts of precession on the waveforms from high-mass sources. These expressions may identify new precessing binary parameters whose waveforms are dissimilar from the existing sample.Comment: 11 figures; v2 includes response to referee suggestion

Intrinsic selection biases of ground-based gravitational wave searches for high-mass BH-BH mergers

The next generation of ground-based gravitational wave detectors may detect a few mergers of comparable-mass M\simeq 100-1000 Msun ("intermediate-mass'', or IMBH) spinning black holes. Black hole spin is known to have a significant impact on the orbit, merger signal, and post-merger ringdown of any binary with non-negligible spin. In particular, the detection volume for spinning binaries depends significantly on the component black hole spins. We provide a fit to the single-detector and isotropic-network detection volume versus (total) mass and arbitrary spin for equal-mass binaries. Our analysis assumes matched filtering to all significant available waveform power (up to l=6 available for fitting, but only l<= 4 significant) estimated by an array of 64 numerical simulations with component spins as large as S_{1,2}/M^2 <= 0.8. We provide a spin-dependent estimate of our uncertainty, up to S_{1,2}/M^2 <= 1. For the initial (advanced) LIGO detector, our fits are reliable for $M\in[100,500]M_\odot$ ($M\in[100,1600]M_\odot$). In the online version of this article, we also provide fits assuming incomplete information, such as the neglect of higher-order harmonics. We briefly discuss how a strong selection bias towards aligned spins influences the interpretation of future gravitational wave detections of IMBH-IMBH mergers.Comment: 18 pages, 15 figures, accepted by PRD. v2 is version accepted for publication, including minor changes in response to referee feedback and updated citation

Chemical fractionation of siderophile elements in impactites from Australian meteorite craters

The abundance pattern of siderophile elements in terrestrial and lunar impact melt rocks was used extensively to infer the nature of the impacting projectiles. An implicit assumption made is that the siderophile abundance ratios of the projectiles are approximately preserved during mixing of the projectile constituents with the impact melts. As this mixture occurs during flow of strongly shocked materials at high temperatures, however there are grounds for suspecting that the underlying assumption is not always valid. In particular, fractionation of the melted and partly vaporized material of the projectile might be expected because of differences in volatility, solubility in silicate melts, and other characteristics of the constituent elements. Impactites from craters with associated meteorites offer special opportunities to test the assumptions on which projectile identifications are based and to study chemical fractionation that occurred during the impact process

Spray Ejected from the Lunar Surface by Meteoroid Impact

Fragments ejected from lunar surface by meteoroid impact analyzed on basis of studies of hypervelocity impact in rock and san

Research core drilling in the Manson impact structure, Iowa

The Manson impact structure (MIS) has a diameter of 35 km and is the largest confirmed impact structure in the United States. The MIS has yielded a Ar-40/Ar-39 age of 65.7 Ma on microcline from its central peak, an age that is indistinguishable from the age of the Cretaceous-Tertiary boundary. In the summer of 1991 the Iowa Geological Survey Bureau and U.S. Geological Survey initiated a research core drilling project on the MIS. The first core was beneath 55 m of glacial drift. The core penetrated a 6-m layered sequence of shale and siltstone and 42 m of Cretaceous shale-dominated sedimentary clast breccia. Below this breccia, the core encountered two crystalline rock clast breccia units. The upper unit is 53 m thick, with a glassy matrix displaying various degrees of devitrification. The upper half of this unit is dominated by the glassy matrix, with shock-deformed mineral grains (especially quartz) the most common clast. The glassy-matrix unit grades downward into the basal unit in the core, a crystalline rock breccia with a sandy matrix, the matrix dominated by igneous and metamorphic rock fragments or disaggregated grains from those rocks. The unit is about 45 m thick, and grains display abundant shock deformation features. Preliminary interpretations suggest that the crystalline rock breccias are the transient crater floor, lifted up with the central peak. The sedimentary clast breccia probably represents a postimpact debris flow from the crater rim, and the uppermost layered unit probably represents a large block associated with the flow. The second core (M-2) was drilled near the center of the crater moat in an area where an early crater model suggested the presence of postimpact lake sediments. The core encountered 39 m of sedimentary clast breccia, similar to that in the M-1 core. Beneath the breccia, 120 m of poorly consolidated, mildly deformed, and sheared siltstone, shale, and sandstone was encountered. The basal unit in the core was another sequence of sedimentary clast breccia. The two sedimentary clast units, like the lithologically similar unit in the M-1 core, probably formed as debris flows from the crater rim. The middle, nonbrecciated interval is probably a large, intact block of Upper Cretaceous strata transported from the crater rim with the debris flow. Alternatively, the sequence may represent the elusive postimpact lake sequence

Effects of electrical charging on the mechanical Q of a fused silica disk

We report on the effects of an electrical charge on mechanical loss of a fused silica disk. A degradation of Q was seen that correlated with charge on the surface of the sample. We examine a number of models for charge damping, including eddy current damping and loss due to polarization. We conclude that rubbing friction between the sample and a piece of dust attracted by the charged sample is the most likely explanation for the observed loss.Comment: submitted to Review of Scientific Instrument