Southern Africa is characterised by unusually elevated topography and abnormal heat flow. This can be explained by thermal perturbation of the mantle, but the origin of this is unclear. Geophysics has not detected a thermal anomaly in the upper mantle and there is no geochemical evidence of an asthenosphere mantle contribution to the Cenozoic volcanic record of the region. Here we show that natural CO2 seeps along the Ntlakwe-Bongwan fault within KwaZulu-Natal, South Africa, have C-He isotope systematics that support an origin from degassing mantle melts. Neon isotopes indicate that the melts originate from a deep mantle source that is similar to the mantle plume beneath Reunion, rather than the convecting upper mantle or sub-continental lithosphere. This confirms the existence of the Quathlamba mantle plume and importantly provides the first evidence in support of upwelling deep mantle beneath Southern Africa, helping to explain the regions elevation and abnormal heat flow.

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Noble gases confirm plume-related mantle degassing beneath Southern Africa.

The purpose of this ISRM Suggested Method is to describe a methodology for in situ microseismic monitoring of the rock mass fracturing processes occurring as a result of excavations for rock slopes, tunnels, or large caverns in the fields of civil, hydraulic, or mining engineering. In this Suggested Method, the equipment that is required for a microseismic monitoring system is described; the procedures are outlined and illustrated, together with the methods for data acquisition and processing for improving the monitoring results. There is an explanation of the methods for presenting and interpreting the results, and recommendations are supported by several examples.

ISRM Suggested Method for In Situ Microseismic Monitoring of the Fracturing Process in Rock Masses

A new seismic-based strain energy methodology for coal burst forecasting in underground coal mines

The Earthquake Model of Middle East (EMME) project was carried out between 2010 and 2014 to provide a harmonized seismic hazard assessment without country border limitations. The result covers eleven countries: Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Jordan, Lebanon, Pakistan, Syria and Turkey, which span one of the seismically most active regions on Earth in response to complex interactions between four major tectonic plates i.e. Africa, Arabia, India and Eurasia. Destructive earthquakes with great loss of life and property are frequent within this region, as exemplified by the recent events of Izmit (Turkey, 1999), Bam (Iran, 2003), Kashmir (Pakistan, 2005), Van (Turkey, 2011), and Hindu Kush (Afghanistan, 2015). We summarize multidisciplinary data (seismicity, geology, and tectonics) compiled and used to characterize the spatial and temporal distribution of earthquakes over the investigated region. We describe the development process of the model including the delineation of seismogenic sources and the description of methods and parameters of earthquake recurrence models, all representing the current state of knowledge and practice in seismic hazard assessment. The resulting seismogenic source model includes seismic sources defined by geological evidence and active tectonic findings correlated with measured seismicity patterns. A total of 234 area sources fully cross-border-harmonized are combined with 778 seismically active faults along with background-smoothed seismicity. Recorded seismicity (both historical and instrumental) provides the input to estimate rates of earthquakes for area sources and background seismicity while geologic slip-rates are used to characterize fault-specific earthquake recurrences. Ultimately, alternative models of intrinsic uncertainties of data, procedures and models are considered when used for calculation of the seismic hazard. At variance to previous models of the EMME region, we provide a homogeneous seismic source model representing a consistent basis for the next generation of seismic hazard models within the region.

The 2014 Earthquake Model of the Middle East: seismogenic sources

Most probabilistic seismic‐hazard analysis procedures require that at least three seismic source parameters be known, namely the mean seismic activity rate λ , the Gutenberg–Richter b ‐value, and the area‐characteristic (seismogenic source) maximum possible earthquake magnitude m max. In almost all currently used seismic‐hazard assessment procedures that utilize these three parameters, it is explicitly assumed that all three remain constant over time and space. However, closer examination of most earthquake catalogs has indicated that significant spatial and temporal variations existed in the seismic activity rate λ , as well as in the Gutenberg–Richter b ‐value. In this study, the maximum likelihood estimation of these earthquake hazard parameters considers the incompleteness of the catalogs, the uncertainty in the earthquake magnitude determination, as well as the uncertainty associated with the applied earthquake‐occurrence models. The uncertainty in the earthquake‐occurrence models is introduced by assuming that both the mean seismic activity rate λ and the Gutenberg–Richter b ‐value are random variables, each described by the gamma distribution. This approach results in the extension of the classic frequency–magnitude Gutenberg–Richter relation and the Poisson distribution of the number of earthquakes with their compounded counterparts (Benjamin, 1968; Campbell, 1982, 1983). The proposed procedure was applied in the estimation of the seismicity parameters in an area that had experienced the strongest and most devastating earthquake in contemporary South African history, namely the 29 September 1969 M w 6.3 Ceres–Tulbagh event. In this example, it was shown that the introduction of uncertainty in the earthquake‐occurrence model reduced the mean return periods, leading to an increase of the estimated seismic hazard. Additionally, this study confirmed that accounting for magnitude uncertainties had the opposite effect, that is, it brought about increases in the return periods, or, equivalently, a reduction of the estimated seismic hazard.

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Estimation of Earthquake Hazard Parameters from Incomplete Data Files. Part III. Incorporation of Uncertainty of Earthquake-Occurrence Model

Several procedures for the statistical estimation of the regioncharacteristic maximum possible earthquake magnitude, mmax , are currently available. This paper aims to introduce and compare the 12 existing procedures. For each of the procedures given, there are notes on its origin, assumptions made in its derivation, condition for validity, weak and strong points, etc. The applicability of each particular procedure is determined by the assumptions of the model and/or the available information on seismicity of the area.

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Statistical tools for maximum possible earthquake magnitude estimation

should be reviewed; surface and subsurface investigations of the orientation, geometry, sense of displacement, and length of ruptures should be conducted; and the possibility of multiple ruptures ought to be assessed. Seismotectonic models have not yet been developed for South Africa. The delineation of seismotectonic zones of Africa as part of the Global Seismic Hazard Assessment Program (GSHAP) in 1999 was based on an analysis of the main tectonic structures and a correlation with present-day seismicity. Because of the large scale of the GSHAP project, only regional structures were accounted for in the preparation of the source zones. Our study was initiated to remedy this knowledge gap. We have completed four steps, which are described in this paper. Compilation of a catalog of earthquake activity that has

http://africaarray.psu.edu/publications/pdfs/singh.pdf

Seismotectonic Models for South Africa: Synthesis of Geoscientific Information, Problems, and the Way Forward

A first-order seismotectonic model was created for South Africa. This was done using four logical steps: geoscientific data collection, characterisation, assimilation and zonation. Through the definition of subunits of concentrations of earthquake foci and large neotectonic and structural domains, seismotectonic structures, systems and domains were created. Relatively larger controls of seismicity exist between the Great Escarpment and the coast. In the south, this region is characterised by large aeromagnetic anomalies and large EW trending faults. In the west, it is characterised by the NW-SE trending Wegener stress anomaly, radial-trending dykes and earthquake clusters. In the east, it is character- ised by a large neotectonic domain where several large historical earthquakes occurred. In the centre of South Africa, several clusters of earthquake activity are found, often related to mining activity. Further north, seismicity is related to both mining activity and neotectonic deformation. This work contributes to the development of a seismotectonic model for South Africa by (1) bringing together, digitally, several data sets in a common GIS plat- form (geology, geophysics, stress, seismicity, neotectonics, topography, crustal and mantle structure and anisotropy), (2) understanding the significance of data sets for seismotectonic zonation and limitations thereof and (3) obtaining a reasonable regional model for use in seismic hazard assessments.

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First-order regional seismotectonic model for South Africa

An atlas of isoseismal maps for South Africa, dating from as far back as 1932–2005, is provided This work involved searching through historical reports to find records of macroseismic effects In many instances, when there was a large tremor, questionnaires were distributed to local towns to assess the severity of the tremor and the damage it caused Based on the results of these questionnaires and site investigations, isoseismal maps were drawn These isoseismal maps were revisited and digitised for this study Five additional isoseismal maps were prepared by the authors based on the results of questionnaires alone Most isoseismal maps in the historical record use the Modified Mercalli scale All maps are hence provided according to this scale

Short communication: collection of isoseismal maps for South Africa

Earthquake motion is one of the extreme loads acting on large dams. Dam owners and regulators must therefore ensure that dams are safely operated and present minimal risk to the public in case of extreme loads such as floods and earthquakes. Owners of many dams or officials in charge of dam safety programs may consider comparative assessment of the seismic risk associated with their dams and establish priorities for detailed evaluation. South Africa has in excess of 100 large state-owned dams and the characteristics of these dams have been used to perform a basic seismic hazard assessment and rank the vulnerability of these dams from the lowest to highest. One of the most decisive factors that contributes to the risk of a dam is the wall type; with gravity and earthfill dams being the most vulnerable to earthquake motion. Another aspect that needs further investigation is the downstream hazard potential which, if known to a better degree of accuracy, can provide more reasonable estimates of the risk factors.

Mayshree Singh

Papers

Statistical tools for maximum possible earthquake magnitude estimation

Seismotectonic Models for South Africa: Synthesis of Geoscientific Information, Problems, and the Way Forward

First-order regional seismotectonic model for South Africa

Short communication: collection of isoseismal maps for South Africa

Seismic Risk Ranking for Large Dams in South Africa