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We present a method for measuring the dispersion of higher mode surface wave phase velocities from a single seismogram using a hierarchical transdimensional Bayesian approach. The 1-D shear velocity profiles down to 800 km depth between sources and seismic stations are regarded as the controlling parameters to tune the phase velocities of fundamental and higher modes. The misfits between synthetics and real waveforms indicate whether the phase velocities are recovered well from the data. We use Monte Carlo Markov chains to approximate the posterior distribution of each model parameters and assess the uncertainties from these probability density functions. These techniques can test models of varying dimensions while being parsimonious, thereby letting the data themselves control the complexity of the solution. Another advantage is that the algorithm can decide how much data noise is needed in order to explain the data without overfitting them. The data noise can be treated as an unknown and different noise levels can be applied to the different time windows considered. The posterior noise distributions can then be used as an indicator of the quality of the waveform fit within each frequency–time window. We considered phase velocities between 50 and 200 s for each mode and performed a reliability analysis to determine which modes and periods are reliably constrained. In this paper, we first present the method and demonstrate its feasibility with synthetic tests, which show that the technique is robust. We then illustrate it with applications to real data. We applied the method to two paths sampling Australia using earthquakes at regional distances and obtained results that agree well with previous studies. The new method can be used in regional and global tomographic studies to obtain phase velocity maps and 3-D models of seismic velocities and anisotropy at depths that are not well resolved by fundamental mode surface waves or body waves. [ABSTRACT FROM AUTHOR]

In the absence of quantitative relationships, a cross-gradient function can be used to correlate unknown physical properties in a joint inversion of geophysical data sets. It introduces a structural correlation between properties. A commonly used, inexact approach adds a weighted cross-gradient term as a penalty to the cost function being minimized during inversion. This weighting factor needs to be tuned to balance the regularization and cross-gradient terms. In this paper we propose nonlinear weighting for the cross-gradient function which addresses the very different magnitudes of the cross-gradient and regularization terms. This approach also couples the weighting factors for the regularization and correlation terms reducing the number of tuning parameters. The approach is investigated for a synthetic case. Results are also shown for the 3-D joint inversion of high-resolution magnetic and gravity anomaly data from Southern Queensland in Australia with over 30 million cells. [ABSTRACT FROM AUTHOR]

We present a new S-wave velocity tomographic model of the upper mantle beneath the Australian Plate and its boundaries that we call Aus22. It includes azimuthal anisotropy and was constrained by waveforms from 0.9 million vertical-component seismograms, with the densest data sampling in the hemisphere centred on the Australian continent, using all available data covering this hemisphere. Waveform inversion extracted structural information from surface waves, S- and multiple S-waves and constrained S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle, down to the 660-km discontinuity. The model was validated by resolution tests and, for particular locations in Australia with notable differences from previous models, independent inter-station measurements of surface-wave phase velocities. Aus22 can be used to constrain the structure and evolution of the Australian Plate and its boundaries in fine detail at the regional scale. Thick, high-velocity (and, by inference, cold) cratonic lithosphere occupies nearly all of western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it collides with island arcs, without subducting. Diamondiferous kimberlites and lamproite deposits are underlain by cratonic lithosphere, except for the most recent diamondiferous lamproites in the King Leopold Orogen. The rugged eastern boundary of the cratonic lithosphere resolved by the model provides a lithospheric definition of the Tasman Line. Just east of the Tasman Line, an area of intermediate-thick lithosphere is observed in the southern part of the continent. The eastern part of Australia is underlain by thin, warm lithosphere, evidenced by low seismic velocities. All the sites of Cenozoic intraplate volcanism in eastern Australia are located on thin lithosphere. A low-velocity anomaly is present in the mantle transition zone (410–660 km depths) beneath the Lord Howe and Tasmanid hotspots, indicative of anomalously high temperature and consistent with a deep mantle upwelling feeding these hotspots and, possibly, also the East Australia hotspot. High seismic velocities at 200–410 km depth below New Guinea indicate the presence of slab fragments, probably linked to the subduction of the Australian Plate. High seismic velocities are observed in the transition zone below northeast Australia and indicate the presence of subducted lithospheric fragments trapped in the transition zone, possibly parts of the former northern continental margin of Australia. [ABSTRACT FROM AUTHOR]

In recent years, there has been a considerable expansion of deployments of portable seismic stations across Australia, which have been analysed by receiver function or autocorrelation methods to extract estimates of Moho depth. An ongoing program of full-crustal reflection profiles has now provided more than 25 000 km of reflection transects that have been interpreted for Moho structure. The Moho data set is further augmented by extensive marine reflection results. These new data sources have been combined with earlier refraction and receiver function results to provide full continental coverage, though some desert areas remain with limited sampling. The dense sampling of the Moho indicates the presence of rapid changes in Moho depth, and so, the Moho surface has been constructed using an approach that allows different weighting and spatial influence depending on the nature of the estimate. The inclusion of Moho results from continental-wide gravity inversion with low weighting helps to resolve the continent-ocean transition and to provide additional control in the least sampled zones. The refined distribution indicates the presence of widespread smaller-scale variations in Moho structure. Strong lateral contrasts in crustal thickness remain, but some have become more subdued with improved sampling of critical areas. The main differences from earlier results lie in previously poorly sampled regions around the Lake Eyre Basin, where additional passive seismic results indicate somewhat thicker crust though still with a strong contrast in crustal thickness to the cratonic zone to the west. [ABSTRACT FROM AUTHOR]

Most studies of sea level budget only indicate the stationary causes for the global mean sea level (GMSL) rise over the course of a time span of interest, providing limited information on temporary changes in the GMSL budget. In this contribution, we present an instantaneous budget of the GMSL for the period of 2003–2015, which offers new insights on the time evolution of the GMSL budget. We use a space-state model to compute the instantaneous rates of GMSL and their contributing sources (barystatic and steric contributions), to investigate the causes of the GMSL instantaneous budget, which accounts for and quantifies low-frequency variations in GMSL rise. Combining the barystatic GMSL instantaneous rates (estimated from satellite gravimetry) along with a particular choice of steric GMSL instantaneous rates (inferred from an Argo product) achieves closure of the GMSL instantaneous budget with a standard deviation of 0.4 mm yr−1. We find that the barystatic GMSL rate is primarily responsible for the striking fluctuations in the GMSL instantaneous rates between 2009 and 2015. For example, over only 20 months (July 2010 to February 2012), the GMSL (barystatic) rate increases from 0.32 (0.71) to 6.12 (4.55) mm yr−1. These strong fluctuations mainly result from hydrology and mountain glacier mass variations rather than mass loss in ice sheet, for instance, Australia slowed ∼1.2 mm yr−1 equivalent contribution to GMSL rise over the year 2010, which is approximately four times the linear rate of Antarctica mass loss. [ABSTRACT FROM AUTHOR]

Gravity gradient tensors (GGTs) are used to investigate the density of subsurface structures in the Earth's crust and can reduce ambiguity during data interpretation. However, costs and research area restrictions often prevent their application during surveys, thereby limiting their utility. To address this limitation, a matrix equation based on the Taylor series expansion that uses the gravity vector and its neighbours was formulated to obtain the GGTs. Higher-order derivatives of the gravity vector were utilized to constrain the calculation, which improved the accuracy of the transformation. Synthetic data were used to demonstrate that the proposed approach improved accuracy when the radial component of the gravity vector was transformed into GGTs. This approach was also applied to gravity data from the Otway Basin in Australia. Compared with the measured GGT, the results obtained using the proposed approach had a relative error of 0.46. [ABSTRACT FROM AUTHOR]

The equivalent source technique is a powerful and widely used method for processing gravity and magnetic data. Nevertheless, its major drawback is the large computational cost in terms of processing time and computer memory. We present two techniques for reducing the computational cost of equivalent source processing: block-averaging source locations and the gradient-boosted equivalent source algorithm. Through block-averaging, we reduce the number of source coefficients that must be estimated while retaining the minimum desired resolution in the final processed data. With the gradient-boosting method, we estimate the sources coefficients in small batches along overlapping windows, allowing us to reduce the computer memory requirements arbitrarily to conform to the constraints of the available hardware. We show that the combination of block-averaging and gradient-boosted equivalent sources is capable of producing accurate interpolations through tests against synthetic data. Moreover, we demonstrate the feasibility of our method by gridding a gravity data set covering Australia with over 1.7 million observations using a modest personal computer. [ABSTRACT FROM AUTHOR]

Observations from different disciplines have shown that our planet is highly heterogeneous at multiple scale lengths. Still, many seismological Earth models tend not to include any small-scale heterogeneity or lateral velocity variations, which can affect measurements and predictions based on these homogeneous models. In this study, we describe the lithospheric small-scale isotropic heterogeneity structure in terms of the intrinsic, diffusion and scattering quality factors, as well as an autocorrelation function, associated with a characteristic scale length (a) and RMS fractional velocity fluctuations (ε). To obtain this characterization, we combined a single-layer and a multilayer energy flux models with a new Bayesian inference algorithm. Our synthetic tests show that this technique can successfully retrieve the input parameter values for 1- or 2-layer models and that our Bayesian algorithm can resolve whether the data can be fitted by a single set of parameters or a range of models is required instead, even for very complex posterior probability distributions. We applied this technique to three seismic arrays in Australia: Alice Springs array (ASAR), Warramunga Array (WRA) and Pilbara Seismic Array (PSAR). Our single-layer model results suggest intrinsic and diffusion attenuation are strongest for ASAR, while scattering and total attenuation are similarly strong for ASAR and WRA. All quality factors take higher values for PSAR than for the other two arrays, implying that the structure beneath this array is less attenuating and heterogeneous than for ASAR or WRA. The multilayer model results show the crust is more heterogeneous than the lithospheric mantle for all arrays. Crustal correlation lengths and RMS velocity fluctuations for these arrays range from ∼0.2 to 1.5 km and ∼2.3 to 3.9 per cent, respectively. Parameter values for the upper mantle are not unique, with combinations of low values of the parameters (a < 2 km and ε < ∼2.5 per cent) being as likely as those with high correlation length and velocity variations (a > 5 km and ε > ∼2.5 per cent, respectively). We attribute the similarities in the attenuation and heterogeneity structure beneath ASAR and WRA to their location on the proterozoic North Australian Craton, as opposed to PSAR, which lies on the archaean West Australian Craton. Differences in the small-scale structure beneath ASAR and WRA can be ascribed to the different tectonic histories of these two regions of the same craton. Overall, our results highlight the suitability of the combination of an energy flux model and a Bayesian inference algorithm for future scattering and small-scale heterogeneity studies, since our approach allows us to obtain and compare the different quality factors, while also giving us detailed information about the trade-offs and uncertainties in the determination of the scattering parameters. [ABSTRACT FROM AUTHOR]

Seismic full waveform inversion (FWI) is a state-of-the-art technique for estimating subsurface physical models from recorded seismic waveform, but its application requires care because of high non-linearity and non-uniqueness. The final outcome of global convergence from conventional FWI using local gradient information relies on an informative starting model. Bayesian inference using Markov chain Monte Carlo (MCMC) sampling is able to remove such dependence, by a direct extensive search of the model space. We use a Bayesian trans-dimensional MCMC seismic FWI method with a parsimonious dipping layer parametrization, to invert for subsurface velocity models from pre-stack seismic shot gathers that contain mainly reflections. For the synthetic study, we use a simple four-layer model and a modified Marmousi model. A recently collected multichannel off-shore seismic reflection data set, from the Lord Howe Rise (LHR) in the east of Australia, is used for the field data test. The trans-dimensional FWI method is able to provide model ensembles for describing posterior distribution, when the dipping-layer model assumption satisfies the observed data. The model assumption requires narrow models, thus only near-offset data to be used. We use model stitching with lateral and depth constraints to create larger 2-D models from many adjacent overlapping submodel inversions. The inverted 2-D velocity model from the Bayesian inference can then be used as a starting model for the gradient-based FWI, from which we are able to obtain high-resolution subsurface velocity models, as demonstrated using the synthetic data. However, lacking far-offset data limits the constraints for the low-wavenumber part of the velocity model, making the inversion highly non-unique. We found it challenging to apply the dipping-layer based Bayesian FWI to the field data. The approximations in the source wavelet and forward modelling physics increase the multimodality of the posterior distribution; the sampled velocity models clearly show the trade-off between interface depth and velocity. Numerical examples using the synthetic and field data indicate that trans-dimensional FWI has the potential for inverting earth models from reflection waveform. However, a sparse model parametrization and far offset constraints are required, especially for field application. [ABSTRACT FROM AUTHOR]

The degree to which the lowermost mantle influences behaviour of the geodynamo has been debated over the past quarter century. Our analysis of a comprehensive set of 17 Cenozoic palaeomagnetic transitional field records obtained from lavas in the Southern Hemisphere provides robust evidence of stable mantle control since the Pliocene. The records come from a region where—given a significantly weakened axial dipole—the magnetic field today would be largely controlled by the non-axial dipole (NAD) flux patch currently emanating from Earth's outer core beneath western Australia. The palaeomagnetic recording sites from west to east include the south Indian Ocean, eastern Australia, New Zealand and French Polynesia. The analysed records contain from 2 to 26 sequential transitional virtual geomagnetic poles (VGPs). 10 of the 17 records supply at least one VGP within a narrow longitudinal band 10°-wide between 60°S and the equator, centred along 102.4°E. That is, transitional data from 59 per cent of the Cenozoic recordings are found to reside in a region that encompasses a mere 2.8 per cent of the VGP transitional area on Earth's surface. A robust Monte Carlo approach applied to this data set, one that takes into account the number of transitional VGPs contained in each record, finds this result highly improbable (p-value  = 0.0006). The present-day pattern of vertical flux at the core–mantle boundary shows an anomalously strong, thin Southern Hemisphere longitudinal band off the west coast of Australia that strikingly coincides with this unusual palaeomagnetic finding. We conclude with a high degree of confidence that this band of flux has remained virtually unmoved for at least the past 3 Myr. Seemingly independent of the behaviour of the axial dipole, our findings indicate that it has dominated the magnetic field over an area of considerable size during attempts by the geodynamo to reverse polarity. [ABSTRACT FROM AUTHOR]

We propose a new framework for incorporating petrophysical and geological information into voxel-based geophysical inversion. By developing the geophysical inverse problem from a probabilistic perspective, we redesign the objective function and the iteration steps as a suite of cyclic optimization problems in which three separate MAP optimization problems are solved using geophysical, petrophysical and geological data, respectively. By quantitatively linking these data into a single framework, we recover a final inverted model that reproduces the observed, or desired, petrophysical and geological features while fitting the geophysical data. To achieve our goal we replace the Gaussian prior, used in the Tikhonov inversion approach, by a Gaussian mixture model. After each geophysical model update, the mixture parameters (means, variances and proportions) are determined by the geophysical model and the expected characteristics of the lithologies through another optimization process using the expectation–maximization algorithm. We then classify the model cells into rock units according to the petrophysical and geological information. These two additional steps over the petrophysical and geological data result in a dynamic update of the reference model and associated weights and guide the inversion towards reproducing the expected petrophysical and geological characteristics. The resulting geophysical objective function does not require extra terms to include the additional petrophysical and geological information; this is an important distinction between our work and previous frameworks that carry out joint geophysical and petrophysical data inversion. We highlight different capabilities of our methodology by inverting magnetotelluric and direct-current resistivity data in 1-D and 2-D, respectively. Finally, we apply our framework to inverting airborne frequency domain data, acquired in Australia, for the detection and characterization of saline contamination of freshwater. [ABSTRACT FROM AUTHOR]

The variation of temperature in the crust is difficult to quantify due to the sparsity of surface heat flow observations and lack of measurements on the thermal properties of rocks at depth. We examine the degree to which the thermal structure of the crust can be constrained from the Curie depth and surface heat flow data in Southeastern Australia. We cast the inverse problem of heat conduction within a Bayesian framework and derive its adjoint so that we can efficiently find the optimal model that best reproduces the data and prior information on the thermal properties of the crust. Efficiency gains obtained from the adjoint method facilitate a detailed exploration of thermal structure in SE Australia, where we predict high temperatures within Precambrian rocks of 650 °C due to relatively high rates of heat production (0.9–1.4 μW m−3). In contrast, temperatures within dominantly Phanerozoic crust reach only 520 °C at the Moho due to the low rates of heat production in Cambrian mafic volcanics. A combination of the Curie depth and heat flow data is required to constrain the uncertainty of lower crustal temperatures to ±73 °C. We also show that parts of the crust are unconstrained if either data set is omitted from the inversion. [ABSTRACT FROM AUTHOR]

The 280-km-long San Cristobal Trough (SCT), created by the tearing of the Australia plate as it subducts under the Pacific Plate near the Solomon and Vanuatu subduction zones, has hosted strike-slip earthquake sequences in 1993 and 2015. Both sequences, which likely represent a complete seismic cycle, began along the oldest section of the SCT—the portion farthest from the tear that has experienced the most cumulative displacement—and migrated to the younger sections closer to the tear. The SCT's abundant seismicity allows us to study transform boundary development—a process rarely observed along a single fault system—through observations of earthquake rupture properties. Using the spectral ratio method based on empirical Green's functions (EGFs), we calculate the corner frequencies of three M w ∼7 2015 earthquakes and colocated smaller earthquakes. We utilize two different spectral ratio stacking methods and fit both Brune and Boatwright models to the stacked spectral ratios. Regardless of stacking methods and spectral models, we find that the corner frequencies of the 2015 M w ∼7 earthquakes decrease slightly with distance from the tear. Assuming a constant rupture velocity and an omega-square spectral model, this corner frequency decrease may be due to an increase in rupture length with distance from the tear. The spectrum of the 2015 earthquake farthest from the tear also deviates from the omega-square model, which may indicate rupture complexity. Stress drop estimates from the corner frequencies of the 2015 M w ∼7 earthquakes range between 1 and 7 MPa, whereas stress drop estimates of their EGFs range from ∼0.05 to 10 MPa with most values between 0.1 and 1 MPa. Independent evidence from a second moments analysis of the 2015 earthquake sequence also indicates a possible increase in rupture length with distance from the tear, confirming the results from the spectral ratio analysis. We also observe an increase in normalized centroid time-delay values, a first-order proxy for rupture behaviour, with distance from the tear for the 2015 sequence. A similar trend for the 1993 sequence suggests that earthquake rupture varies systematically along the SCT. Since distance from the tear corresponds to cumulative fault displacement, these along-strike rupture variations may be due to a displacement-driven fault maturation process. [ABSTRACT FROM AUTHOR]

We apply virtual deep seismic sounding (VDSS) to data collected from both permanent and temporary seismic stations in Australia with the goal of examining (i) the resilience of the method to the presence of complex lithospheric structure and (ii) the effectiveness of different approaches for estimating bulk crustal properties (namely thickness and Vp). Data from the permanent station WRAB in the Northern Territory is ideal for benchmarking VDSS (large number and favourable distribution of recorded earthquakes), with the results from several approaches agreeing on a thickness of 40–42 km. Application of VDSS to data from the temporary BILBY array, a linear distribution of broadband stations that traverses central Australia, shows that strong Moho reflections can be retrieved with as few as two earthquakes even at the transition between crustal blocks of different character and in the presence of thick sedimentary basins. Crustal thickness varies between 36 and 54 km and compares well with the reflectivity character of nearby deep seismic reflection lines. Furthermore, we find that off-line estimates of crustal thickness, calculated by binning the source regions according to back-azimuth, produce values of crustal thickness that are consistent with the regional geology. Overall, we find that VDSS is a powerful technique for estimating crustal thickness and velocity due to its insensitivity to complex short-wavelength structure and requirement of a small number earthquakes to produce a stable result. However, not all schemes tested for extracting bulk crustal properties appear to be robust and stringent data quality checking is still required during implementation. [ABSTRACT FROM AUTHOR]

Conventional full-waveform inversion (FWI) often fails to retrieve the unknown model parameters from noisy seismic data. A successful FWI implementation usually requires to follow a multistage recovery approach, starting from the retrieval of the lower model wavenumbers (tomography) to those with the higher resolutions (migration). Here, we propose a new method based on the flux-corrected transport (FCT) technique often used in computational fluid dynamics for the removal of instabilities in a shock profile. FCT involves three finite-difference steps: a transport, a diffusion and an antidiffusion process. This third step involves non-linear operators such as maximum and minimum, which are non-differentiable in a classic sense. However, since the seismic source wavelet and the corresponding wavefield are relatively smooth and continuous in nature without any strong ripples like shock waves, we exclude the non-linear step from FCT, which allows us to evaluate the novel FWI gradient efficiently. As a result, we achieve a converging FWI model by gradually reducing the diffusive flux-correction. We demonstrate the versatility of FCT-based FWI on a noisy synthetic data set from the Marmousi II model and a marine field data set from offshore Australia. [ABSTRACT FROM AUTHOR]

Debate is ongoing as to which tectonic model is most consistent with the known geology of southeast Australia, formerly part of the eastern margin of Gondwana. In particular, numerous tectonic models have been proposed to explain the enigmatic geological relationship between Tasmania and the mainland, which is separated by Bass Strait. One of the primary reasons for the lack of certainty is the limited exposure of basement rocks, which are masked by the sea and thick Mesozoic–Cenozoic sedimentary and volcanic cover sequences. We use ambient noise tomography recorded across Bass Strait to generate a new shear wave velocity model in order to investigate crustal structure. Fundamental mode Rayleigh wave phase velocity dispersion data extracted from long-term cross-correlation of ambient noise data are inverted using a transdimensional, hierarchical, Bayesian inversion scheme to produce phase velocity maps in the period range 2–30 s. Subsequent inversion for depth-dependent shear wave velocity structure across a dense grid of points allows a composite 3-D shear wave velocity model to be produced. Benefits of the transdimensional scheme include a data-driven parametrization that allows the number and distribution of velocity unknowns to vary, and the data noise to also be treated as an unknown in the inversion. The new shear wave velocity model clearly reveals the primary sedimentary basins in Bass Strait as slow shear velocity zones which extend down to 14 km in depth. These failed rift basins, which formed during the early stages of Australia–Antarctica break-up, appear to be overlying thinned crust, where high velocities of 3.8–4.0 km s−1 occur at depths greater than 20 km. Along the northern margin of Bass Strait, our new model is consistent with major tectonic boundaries mapped at the surface. In particular, we identify an east dipping velocity transition zone in the vicinity of the Moyston Fault, a major tectonic boundary between the Lachlan and Delamerian orogens, which are part of the Phanerozoic accretionary terrane that makes up eastern Australia. A pronounced lineament of high shear wave velocities (∼3.7–3.8 km s−1) in the lower crust of our new model may represent the signature of relict intrusive magmatism from failed rifting in the early stages of Australia–Antarctica break-up along a crustal scale discontinuity in the Selwyn Block microcontinent which joins Tasmania and Victoria. [ABSTRACT FROM AUTHOR]

Different mechanisms have been proposed as explanations for seismic anisotropy at the base of the mantle, including crystallographic preferred orientation of various minerals (bridgmanite, post-perovskite and ferropericlase) and shape preferred orientation of elastically distinct materials such as partial melt. Investigations of the mechanism for D" anisotropy usually yield ambiguous results, as seismic observations rarely (if ever) uniquely constrain a mechanism or orientation and usually rely on significant assumptions to infer flow patterns in the deep mantle. Observations of shear wave splitting and polarities of SdS and PdP reflections off the D" discontinuity are among our best tools for probing D" anisotropy; however, currently available data sets cannot constrain one unique scenario among those suggested by the mineral physics literature. In this work, we determine via a forward modelling approach what combinations of body wave phases (e.g. SKS, SKKS and ScS) are required to uniquely constrain a mechanism for D" anisotropy. We test nine models based on single-crystal and polycrystalline elastic tensors provided by mineral physics studies. Our modelling predicts fast shear wave splitting directions for SKS, SKKS and ScS phases, as well as polarities of P- and S- wave reflections off the D" interface, for a range of propagation directions, via solution of the Christoffel equation. We run tests using randomly selected synthetic data sets based on a given starting model, controlling the total number of measurements, the azimuthal distribution, and the type of seismic phases. For each synthetic data set, we search over all possible elastic tensors and orientations to determine which are consistent with the synthetic data. Overall, we find it difficult to uniquely constrain the mechanism for anisotropy with a typical number of seismic anisotropy measurements (based on currently available studies) with only one measurement technique (SKS, SKKS, ScS or reflection polarities). However, data sets that include SKS, SKKS and ScS measurements or a combination of shear wave splitting and reflection polarity measurements increase the probability of uniquely constraining the starting model and its orientation. Based on these findings, we identify specific regions (i.e. North America, northwestern Pacific and Australia) of the lowermost mantle with sufficient ray path coverage for a combination of measurement techniques. [ABSTRACT FROM AUTHOR]