ORCID Profile
0000-0002-4167-4437
Current Organisations
Geoscience Australia
,
Australian National University
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Publisher: Informa UK Limited
Date: 04-04-0012
Publisher: American Geophysical Union (AGU)
Date: 09-2020
DOI: 10.1029/2020JB019808
Publisher: Seismological Society of America (SSA)
Date: 16-03-2023
DOI: 10.1785/0220220348
Abstract: The Australian Seismometers in Schools (AuSIS) network operates 50 broadband seismic stations across Australia that are hosted at schools. The instruments augment the Australian National Seismograph Network providing valuable data from urban and regional Australia. The network coverage is quite sparse, but these vital records of rare, moderate Australian earthquakes can improve our understanding of the deformation within the stable continental region of Australia, especially for events with no surface rupture. In this study, we present the feasibility of identifying the fault plane of moderate earthquakes on the Australian continent, using data from the AuSIS network. We examine the fault plane of the September 2021 Mw 5.9 Woods Point earthquake that occurred about 130 km northeast of the Melbourne metropolitan area. We estimate the hypocenter and the centroid moment tensor (CMT) to identify the fault plane from the auxiliary plane in the focal mechanism. We explore a range of 1D models and a 3D Earth model to simulate seismic arrivals and full waveform data. The hypocenter is resolved using P- and S-wave arrivals in a probabilistic framework and the CMT is derived from full waveform modeling through grid search over a set of trial points around the hypocenter. Our solution suggests the mainshock ruptured the depth of 15 ± 4 km, with a strike-slip mechanism striking 348° north on a nearly vertical plane. The high double-couple percentage of this event indicates a simple rupture that propagated from the south (hypocenter) toward the north (centroid) and remained subsurface. This indicates that the causative fault had a deeper structure than the previously known shallow, northwest–southeast-striking faults of the region. The P and T axes deduced from our fault model are notably aligned with the maximum horizontal crustal stress in the region.
Publisher: Oxford University Press (OUP)
Date: 10-2015
DOI: 10.1093/GJI/GGV338
Publisher: Elsevier BV
Date: 2017
Publisher: GeoScienceWorld
Date: 18-04-2018
DOI: 10.1130/L687.1
Publisher: American Geophysical Union (AGU)
Date: 07-2017
DOI: 10.1002/2017JB014230
Publisher: Seismological Society of America (SSA)
Date: 14-01-2020
DOI: 10.1785/0120190062
Abstract: The 12 February 2013 nuclear test conducted by the Democratic People’s Republic of Korea stands out among other nuclear tests because it produced unusually large transversal motions. Previous studies found various percentages of isotropic components of the seismic moment tensor (MT), which opens up an important question about the reliability of the methods and assumptions we routinely use to recover the seismic MT in the point source approximation. Of particular interest is the data noise model that can be utilized to represent the uncertainty associated with the recorded data. If the noise is not accounted for, this may result in a range of unwanted effects such as overfitting waveform data, and, in turn, it may lead to erroneous conclusions. We thus scrutinize the analyses of the seismic MT of this explosion by performing a thorough analysis of the source depth and time utilizing newly developed Earth structure models to invert seismograms at regional distances at different frequency bands. In addition, we estimate the solution uncertainty within a hierarchical Bayesian framework that allows accounting for noise in the data. Our results show that the resulting MT of this event contains an expectedly large isotropic component (about 70%) and a dip-slip faulting.
Publisher: Wiley
Date: 2020
Publisher: Oxford University Press (OUP)
Date: 31-08-2015
DOI: 10.1093/GJI/GGV291
Publisher: Springer Science and Business Media LLC
Date: 30-05-2019
DOI: 10.1038/S41598-019-44439-1
Abstract: Early detection of the onset of a caldera collapse can provide crucial information to understand their formation and thus to minimize risks for the nearby population and visitors. Here, we analyse the 2007 caldera collapse of Piton de la Fournaise on La Réunion Island recorded by a broadband seismic station. We show that this instrument recorded ultra-long period (ULP) signals with frequencies in the range (0.003–0.01 Hz) accompanied by very-long period (VLP) signals (between 0.02 and 0.50 Hz) prior to and during the caldera formation suggesting it is possible to detect the beginning of the collapse at depth and anticipate its surface formation. Interestingly, VLP wave packets with a similar duration of 20 s are identified prior to and during the caldera formation. We propose that these events could result from repeating piston-like successive collapses occurring through a ring-fault structure surrounding a magma reservoir from the following arguments: the source mechanism from the main collapse, the observations of slow source processes as well as observations from the field and the characteristic ring-fault seismicity.
Publisher: Oxford University Press (OUP)
Date: 30-06-2020
DOI: 10.1093/GJI/GGAA305
Abstract: Seismic moment tensors are an important tool and input variable for many studies in the geosciences. The theory behind the determination of moment tensors is well established. They are routinely and (semi-) automatically calculated on a global scale. However, on regional and local scales, there are still several difficulties h ering the reliable retrieval of the full seismic moment tensor. In an earlier study, we showed that the waveform inversion for seismic moment tensors can benefit significantly when incorporating rotational ground motion in addition to the commonly used translational ground motion. In this study, we test, what is the best processing strategy with respect to the resolvability of the seismic moment tensor components: inverting three-component data with Green’s functions (GFs) based on a 3-D structural model, six-component data with GFs based on a 1-D model, or unleashing the full force of six-component data and GFs based on a 3-D model? As a reference case, we use the inversion based on three-component data and 1-D structure, which has been the most common practice in waveform inversion for moment tensors so far. Building on the same Bayesian approach as in our previous study, we invert synthetic waveforms for two test cases from the Korean Peninsula: one is the 2013 nuclear test of the Democratic People’s Republic of Korea and the other is an Mw 5.4 tectonic event of 2016 in the Republic of Korea using waveform data recorded on stations in Korea, China and Japan. For the Korean Peninsula, a very detailed 3-D velocity model is available. We show that for the tectonic event both, the 3-D structural model and the rotational ground motion, contribute strongly to the improved resolution of the seismic moment tensor. The higher the frequencies used for inversion, the higher is the influence of rotational ground motions. This is an important effect to consider when inverting waveforms from smaller magnitude events. The explosive source benefits more from the 3-D structural model than from the rotational ground motion. Nevertheless, the rotational ground motion can help to better constraint the isotropic part of the source in the higher frequency range.
Publisher: American Geophysical Union (AGU)
Date: 30-06-2020
DOI: 10.1029/2020JB019643
Abstract: Shallow earthquakes in the depth range 0–30 km make up more than 60% of all world's earthquakes. However, resolving their seismic source parameters such as the depth and moment tensor components presents a challenge. Here, we investigate the effect of frequencies higher than 0.025 Hz on centroid‐moment‐tensor inversion for the earthquakes occurring in the top 10 km of the Earth's crust. For a synthetic source located at the depth of 1 km, the maximum litude of ground motion due to a vertical dip‐slip mechanism from the waveforms filtered at 0.01–0.15 Hz is about 1,400 times larger than that filtered at 0.01–0.025 Hz. We quantify the effect of this dramatic difference and other waveform differences by introducing the “balance of litudes” and “waveform similarity” functions for different depths and frequencies. They present a simple and fast way to estimate the resolvability of seismic sources at a given depth and frequency band. For the 20 May 2016, M w = 5.9 Petermann Ranges earthquake in Central Australia analyzed at 0.01–0.025 Hz, a high uncertainty accompanies the estimated source parameters. When the frequency band is 0.01–0.15 Hz, the centroid depth is well constrained at 1 km and the mechanism is a thrust fault striking ~314°N and dipping ~30°NE. These simulations require accurate Earth models. Our result, obtained at higher frequencies, is in a great agreement with various other studies that have been carried out for this earthquake and confirms a 20‐km long, shallow rupture.
Publisher: Elsevier BV
Date: 09-2019
Publisher: Seismological Society of America (SSA)
Date: 09-2014
DOI: 10.1785/0220130199
Publisher: Wiley
Date: 06-03-2017
DOI: 10.1002/9781118786352.WBIEG0875
Abstract: Behavioral geography encompasses a broad field of human geography that became influential during the 1960s and 1970s. It emerged in reaction to the “quantitative turn” associated with the spatial sciences paradigm of the 1950s and 1960s. A fundamental goal of behavioral geography is to understand how and why people perceive environments in the way they do, and how these perceptions influence actual spatial behavior. Behavioral geography, which was largely responsible for introducing behavioralism to human geography, is best thought of as an approach rather than as a separate subdiscipline, given the breadth of philosophical perspectives, research foci, and methodologies that it fostered. Behavioral approaches in human geography were applied to a range of topics, including natural hazards, urban and rural residents' cognition of their built and natural environments, and people's affective belonging to place. Although segments of the approach were criticized for their, inter alia, positivism, lack of scientific rigor, and failure to challenge the status quo of society, the behavioral approach to human geography facilitated a greater engagement with philosophical and epistemological issues, forged productive interactions and relationships with cognate disciplines, and helped lay the conceptual and methodological groundwork for human geographers to engage with contemporary social, environmental, and political issues of public policy relevance.
Publisher: Oxford University Press (OUP)
Date: 30-09-2016
DOI: 10.1093/GJI/GGW370
Publisher: Wiley
Date: 11-2018
DOI: 10.1002/2017TC004708
Publisher: SAGE Publications
Date: 22-11-2017
Abstract: This report considers rural geography scholarship in relation to the field of climate change adaptation. While applied perspectives on the modelling and mapping of the potential impacts of climate change-related hazard events on rural localities continue to be an important research theme, more theoretically sophisticated and interpretivist approaches are providing more challenging understandings of the multi-scalar nature of climate change adaptation processes, from the micro-scale of the farm operator to the global scale of shifting climate regimes. Social constructivism is being deployed to critique taken-for-granted interpretations of the natural processes underlying regionally-specific climate change impacts, further broadening the ontological and epistemological lens of the sub-discipline. Rural geography continues to be a fertile sub-disciplinary field for theoretical and methodological experimentation.
No related grants have been discovered for Babak Hejrani.