Large Seismic Events Research Articles

Multi-Parametric Climatological Analysis Reveals the Involvement of Fluids in the Preparation Phase of the 2008 Ms 8.0 Wenchuan and 2013 Ms 7.0 Lushan Earthquakes

A multi-parametric approach was applied to climatological data before the Ms 8.0 2008 Wenchuan and Ms 7.0 2013 Lushan earthquakes (EQs) in order to detect anomalous changes associated to the preparing phase of those large seismic events. A climatological analysis for seismic Precursor Identification (CAPRI) algorithm was used for the detection of anomalies in the time series of four parameters (aerosol optical depth, AOD; skin temperature, SKT; surface latent heat flux, SLHF and total column water vapour, TCWV). Our results show a chain of processes occurred within two months before the EQs: AOD anomalous response is the earliest, followed by SKT, TCWV and SLHF in the EQs. A close spatial relation between the seismogenic Longmenshan fault (LMSF) zone and the extent of the detected anomalies indicates that some changes occurred within the faults before the EQs. The similarity of time sequence of the anomalies between the four parameters may be related to the same process: we interpret the observed anomalies as the consequence of the upraising of gases from a fluid-rich middle/upper crust along pre-existing seismogenic faults, and of their release into the atmosphere. Our multi-parametric analytical approach is able to capture phenomena related to the preparation phase of strong EQs.

A comparison of characteristic parameters of mining related and tectonic seismic aftershock sequences

The temporal decay pattern of seismicity following rock bursts and large magnitude events is studied for aftershock sequences in several mines in Ontario, Canada. The decay phenomenon is described by the so – called Modified Omori’s law. The dependency of the parameters K, c and p with the magnitude of large mine seismic events is analyzed. A total of eleven mining related seismic sequences, with mainshock magnitudes ranging from 0.5 to 4.0 Mn (Nuttli magnitude scale) and from four different mine environments are examined. Results, including the calculation of the Gutenberg - Richter’s and Reasenberg – Jones parameters b and a’, are compared with previous research in tectonic seismicity using available data from New Zealand, Italy and U.S.A. Further parameters were derived and applied in a correlation study of mining related and tectonic events. The study revealed a good correlation between the productivity parameter a’ and b – values. Particularly, the b – values show significant different number ranges for mining related and tectonic data, which was applied to derive a direct numerical relationship between mining related and tectonic parameters and the aftershock number estimation. Finally, numerical values for the b – values in mining related seismic activity were obtained.

Satellite imaging of the 2015 M7.2 earthquake in the Central Pamir, Tajikistan, elucidates a sequence of shallow strike-slip ruptures of the Sarez-Karakul fault

SUMMARYOn 7 December 2015, a shallow Mw 7.2 strike-slip earthquake struck the Murghab River Valley in the Central Pamirs of Tajikistan. Seismologically this event was similar to a large seismic event in 1911 whose causative fault has never been identified. We measure the displacement field of the 2015 event from satellite observations using Sentinel-1 radar interferometry, Landsat-8 optical pixel-tracking, and surface rupture mapping from high resolution SPOT-6/7 imagery to characterize the role this earthquake rupture plays in the accommodation of strain on its causative structure, the Sarez-Karakul fault. We present geomorphic mapping and interpretations of other Quaternary-active reaches of this fault system, which highlight variable rupture history of the different sections. These sections appear to be separated by inherited bedrock structural boundaries. Significantly, the reaches of the fault northeast and southwest of the 2015 rupture exhibit the freshest morphology prior to 2015, indicative of a more recent rupture than elsewhere. Using new high resolution imagery we map fresh scarps at the northern and southern ends of the Sarez-Karakul fault which may represent this 1911 rupture. To test which of these reaches could have been the source of the elusive 1911 event, we compare synthetic seismograms from three plausible fault sources determined from geomorphology, with observed seismic traces from 1911 at early recording stations throughout Europe. We find that the best fitting fault source is in fact southwest of the 2015 rupture, meaning that we have a record of three distinct recent events on the Sarez-Karakul fault system—two of them instrumentally recorded. Our mapping of these separate events reveals a correlation between their boundaries and the active and inherited thrust and suture systems that intersect the northeast striking left-lateral fault, suggesting structural control over the extents of individual ruptures on the active strike-slip fault.

Prompt elasto-gravity signals (PEGS) and their potential use in modern seismology

An earthquake causes a sudden rock-mass redistribution through fault rupture and generates seismic waves that cause bulk density variations propagating with them. Both processes induce gravity perturbations whose signals propagate with the speed of light and therefore can arrive at remote stations earlier than the fastest elastic P wave. In turn, the gravity perturbations generate secondary seismic sources everywhere within the earth, a part of which around the observation locations can cause ground motion prior to the direct P wave arrival there, too. Recently, these so-called prompt elasto-gravity signals (PEGS) of large seismic events like the 2011 Mw 9.1 Tohoku earthquake have been detected using the data recorded by broadband seismometers and superconducting gravimeters. Though the physics of the PEGS has been well understood, the tools used so far for a realistic modelling of them are complicated and computationally intensive. In this study, we present a new and straightforward approach that solves the full-coupled elasto-gravitational boundary-value problem more accurately, but no more complicated than to compute synthetic seismograms in a conventional way. Using the new tool, we simulate the complete PEGS of the 2011 Tohoku earthquake based on a realistic kinematic finite-fault source model. Furthermore, we present a comprehensive investigation of potential uses of PEGS in modern seismology. As an example, we show particularly that the major source parameters like the moment magnitude, the rupture duration and the focal mechanism of a megathrust earthquake like the 2011 Tohoku earthquake can be estimated robustly using the measured PEGS data.

Operational and geological controls of coupled poroelastic stressing and pore-pressure accumulation along faults: Induced earthquakes in Pohang, South Korea

Coupled poroelastic stressing and pore-pressure accumulation along pre-existing faults in deep basement contribute to recent occurrence of seismic events at subsurface energy exploration sites. Our coupled fluid-flow and geomechanical model describes the physical processes inducing seismicity corresponding to the sequential stimulation operations in Pohang, South Korea. Simulation results show that prolonged accumulation of poroelastic energy and pore pressure along a fault can nucleate seismic events larger than Mw3 even after terminating well operations. In particular the possibility of large seismic events can be increased by multiple-well operations with alternate injection and extraction that can enhance the degree of pore-pressure diffusion and subsequent stress transfer through a rigid and low-permeability rock to the fault. This study demonstrates that the proper mechanistic model and optimal well operations need to be accounted for to mitigate unexpected seismic hazards in the presence of the site-specific uncertainty such as hidden/undetected faults and stress regime.

Assessment and mitigation of seismic risk at the urban scale: an application to the historic city center of Leiria, Portugal

The implementation of a culture of seismic risk preparedness is becoming increasingly critical in Europe as the building stock ages and the awareness about seismic risk rises. In this context, the assessment of the seismic vulnerability of existing buildings, followed by the implementation of appropriate retrofitting solutions, can help to substantially reduce the levels of physical damage and economic impact of future events. The central region of Portugal is particularly susceptible to large seismic events and is characterized by the prevalence of historic masonry buildings. This work aims to validate assessment methods for the risk of historical city centers in order to propose management strategies for municipalities and assess the economic impact of large-scale seismic retrofitting. To do this, an application of these methods was performed on the historical city center of Leiria. An in-depth inspection was performed of the entire center and the results were compiled into a database. Using an index-based seismic vulnerability assessment approach, a vulnerability assessment was made for each building. Based on vulnerability and predicted damage, estimates of human and economic losses were made for the city center before and after retrofitting to justify interventions on a broad scale.

The Rise of Earthquake Correlation Range and the Chains of Earthquakes before Large Seismic Events

The paper summarizes the results of the experiment on advance earthquake forecasting using the Reverse Tracing of Precursors (RTP) algorithm based on the phenomenon of the increase in seismicity correlation range before large earthquakes. During the test period from 2003 to 2019, 28 strong earthquakes occurred in five regions of the world, and 23 of these events fell within the regions and alarm intervals diagnosed by the algorithm. The probability of occasional success in the regions was at most 30% and averaged about 15%. These results confirm the efficiency of the RTP algorithm. The tests have also shown a high degree of nonrandom coincidence of the strong earthquakes and their preceding indicators in the form of the increase in the correlation range—the chains of the earthquakes.

S-Wave Attenuation Field and Seismotectonics of Eastern Anatolia

This work studies the characteristics of seismic coda waves attenuation in Eastern Anatolia. The short-period coda waves from about 400 earthquakes that occurred in Eastern Anatolia between 1989 and 2018 are analyzed. The three-component digital records of seismic events with M ≥ 3.5, recorded at epicentral distances of 10–600 kilometers, are used. S-wave attenuation was estimated from short-period coda envelopes (including those of Lg wave coda) at a frequency of ~1 Hz. The structural features of the S-wave attenuation field in the upper mantle of the Lake Van area are similar to those for other seismoactive zones. The attenuation field is represented by blocks, which have weak attenuation and are subisometric in plan view, and strong attenuation zones; in the case of blocks, attenuation decreases in the direction from the boundaries to the central of these blocks (Q-factor is up to 300–700). Among the zones of strong attenuation, which are usually linearly elongated, the most noticeable are the en echelon zone (north of 39° N), associated with the North Anatolian Fault; here, QS ~ 80–110 (up to QS ~ 60 in the north); and the Bitlis-Zagros fold and thrust belt (QS ~ 60–70). Sources of the strongest earthquakes with M > 6.0, including the 1976 Caldiran–Muradiye and 2011 Van earthquakes, are confined to the boundaries of the blocks. The attenuation field structure corresponds to the velocity field structure: low-velocity anomalies correspond to low-Q zones. Vertically elongated volumes, with which intensive localized seismicity (earthquake swarms) is associated and along which deep fluids can migrate, are revealed. Seismic activation in such volumes precedes large seismic events (for example, the 2011 Van earthquake). It is assumed that such volumes can be interpreted as local seismogenic sources.

Anatomy of a Caldera Collapse: Kīlauea 2018 Summit Seismicity Sequence in High Resolution

AbstractThe 2018 Kīlauea eruption and caldera collapse generated intense cycles of seismicity tied to repeated large seismic (Mw ~ 5) collapse events associated with magma withdrawal from beneath the summit. To gain insight into the underlying dynamics and aid eruption response, we applied waveform‐based earthquake detection and double‐difference location as the eruption unfolded. Here, we augment these rapid results by grouping events based on patterns of correlation‐derived phase polarities across the network. From April 29 to August 6, bracketing the eruption, we used ~2,800 events cataloged by the Hawaiian Volcano Observatory to detect and precisely locate 44,000+ earthquakes. Resulting hypocentroids resolve complex, yet coherent structures, concentrated at shallow depths east of Halema'uma'u crater, beneath the eventual eastern perimeter of surface collapse. Based on a preponderance of dilatational P wave first motions and similarities with previously inferred dike structures, we hypothesize that failure was dominated by coupled shear and crack closure.

Heterogeneities of the Field of S-Wave Attenuation in the Lithosphere of the Caucasus and Their Relationship with Seismicity

We have mapped a short-period S-wave attenuation field of in the lithosphere of the Caucasus. We have used a method based on the analysis of the ratio of the maximum amplitudes for Sn- and Pn-waves. We have processed more than 200 earthquakes records, recorded by the Kislovodsk station (KIV) at distances of ~200–750 km. It is shown that, in general, the highest attenuation of shear waves is observed in the western part of the region. It is established that increased and intermediate attenuation takes place for paths simultaneously crossing rupture zones of the 1988 Spitak (Mw = 6.8) and 1991 Racha (Mw = 7.0) earthquakes. At the same time, the source zone of the 1970 Dagestan earthquake with Mw = 6.8 is characterized by mainly lower attenuation. These data are consistent with an earlier conclusion that deep-seated fluids have been ascending into the Earth’s crust from the uppermost mantle for a few decades after large seismic events, and this process leads to a decrease in attenuation of Sn-waves. A high attenuation zone has been identified in the western part of the region, where, according to instrumental and historical data, no seismic events with M ≥ 6.0 have been recorded. It is assumed that processes of a large earthquake preparation may be taking place here.

Seismicity on tidally active solid-surface worlds

Tidal interactions between planets or stars and the bodies that orbit them dissipate energy in their interiors. The dissipated energy heats the interior and a fraction of that energy will be released as seismic energy. Here we formalize a model to describe the tidally-driven seismic activity on planetary bodies based on tidal dissipation. To constrain the parameters of our model we use the seismic activity of the Moon, driven by tidal dissipation from the Earth-Moon interactions. We then apply this model to predict the amount of seismic energy release and largest seismic events on other moons in our Solar System and exoplanetary bodies. We find that many moons in the Solar System should be more seismically active than the Earth's Moon and many exoplanets should exhibit more seismic activity than the Earth. Finally, we examine how temporal-spatial variations in tidal dissipation manifest as variations in the locations and timing of seismic events on these bodies.

Injection-induced seismicity: strategies for reducing risk using high stress path reservoirs and temperature-induced stress preconditioning

SUMMARYIt is suggested that fluid injection in normal faulting stress regimes can stabilize a reservoir if the stress path is high enough. This stabilization is not seen when the reservoir is significantly cooled as a result of injection. Further, a new strategy is suggested for stimulating reservoirs in shear with a reduced chance of inducing a large magnitude seismic event. The version of this methodology presented here is applicable for reverse faulting stress regimes and involves an initial stress preconditioning stage where the reservoir is cooled and the pressure increase is limited. This process reduces the horizontal total stress and thereby also the differential stress. Next, the reservoir is stimulated with a rapid increase in pore pressure, resulting in shear failure at a lower differential stress than was initially present in the reservoir. Due to the connection seen between the Gutenberg–Richter b-value and differential stress, it is suggested that reservoirs stimulated in this fashion will exhibit higher b-values and thereby also have a reduced chance of hosting a large magnitude event. It is suggested that adaptations of this methodology are applicable to both normal and strike-slip faulting stress regimes.

Experimental Demonstration of Decay Heat Removal by Submerged Feeders in a Full-Scale Test Facility of a Natural Circulation Boiling Water Reactor

Removal of decay heat with nonavailability of active systems is a safety issue especially during station blackout (SBO) in a light water reactor. Passive systems are being incorporated in the new designs of nuclear reactors for this purpose. Some of the advanced reactors such as Indian advanced heavy water reactor (AHWR) have dedicated isolation condensers (ICs) which are submerged in large water pool called gravity driven water pool (GDWP). These ICs remove decay heat from the core by natural circulation cooling and dissipate it to the GDWP by natural convection. There is a concern that cracks may develop in the GDWP if a large seismic event similar to Fukushima type occurs. In that case, the pool water is lost and it can threaten the core coolability because of loss of heat sink. In AHWR, the cracks in the water pool leads to the relocation of the water of the pool to the reactor cavity. Feeders of AHWR are positioned in the reactor cavity. Thus, the water relocated in the cavity, will eventually submerge the feeders and these submerged feeders have the potential to remove the decay heat of the core. However, the feeders are located at a lower elevation as compared to the core, and hence, there is concern on the heat removal capability by the submerged feeders by natural convection. To understand this aspect and to establish the core coolability under the above-mentioned conditions, experiments were performed in a full-scale test facility of AHWR. Experiments showed that the decay heat can be safely removed in natural circulation mode of cooling with heat sink located at lower elevation than the heat source.

ANALYSIS OF RING-SHAPED SEISMICITY STRUCTURES IN THE REGION OF THE NORTHERN CAUCASUS: POSSIBLE PREPARATION FOR LARGE EARTHQUAKES

We have been studying some seismicity characteristics in the region of Northern Caucasus since 1964. It was established that ring-shaped seismicity structure have been formed within depth range of 0–33 km prior to large Racha earthquake of 29.05.1991 (Mw=7,0). Seismicity rings are characterized by threshold magnitude value (Mt) and big axis length (L). Earlier we have obtained correlation dependences of Mt and lgL values on magnitudes of main events Mw for intracontinental earthquakes with mechanisms of reverse and oblique-reverse faulting, prevailing in the region of Northern Caucasus. Using these dependences we estimated magnitudes of large event which could be prepared in the area of ring structure: Mw=7,1±0,2 for the zone of the Racha earthquake. This value is close enough to real magnitude of the event mentioned. New big ring structures were identified at the western outskirt of the Great Caucasus and in the region of the Eastern Caucasus, where large earthquakes are not known according to instrumental and historical data. We estimated magnitudes of possible large earthquakes by characteristics of these structures: Mw=7,0±0,2 and Mw=6,9±0,2 in the regions mentioned respectively. Large seismic event, which probably is prepared at the westernmost part of the Great Caucasus, can represent a special danger due to great density of population and nearness of a few big cities: Krasnodar, Novorossiysk, Sochi etc. It is supposed that ring structures formation is a consequence of geologic systems self-organization, connected with deep-seated fluids migration.

RING-SHAPED SEISMICITY STRUCTURES IN THE REGION OF IRAN: POSSIBLE PREPARATION FOR LARGE EARTHQUAKES

We have been studying some seismicity characteristics in the region of Iran including those connected with preparation for large earthquakes. It was established that ring-shaped seismicity structure have been formed within depth range of 0-33 km prior to large Ezgeleh earthquake of 12.11.2017 (Mw=7,3). Shallow seismicity rings are characterized by threshold magnitude values (Mt1) and big axis lengths (L). Earlier we have obtained correlation dependences of Mt1 and lgL values on magnitudes of main events Mw for intracontinental earthquakes with mechanisms of reverse and oblique-reverse faulting, prevailing in the region of Iran. Using these dependences we estimated magnitude of large event which could be prepared in the area of ring structure: Mw=7,1±0,1 for the zone of the Ezgeleh earthquake. Big ring structures were identified at the south-west, north and east of Iran, where large earthquakes are not known according to instrumental and historical data. We estimated magnitudes of possible large earthquakes by characteristics of these structures: Mw=7,2±0,3, Mw=7,1±0,2 and Mw=6,6±0,1 in the regions mentioned respectively. Large seismic event, which probably is being prepared within the south-western part of Iran, can represent a special danger due to nearness of it’s source to the nuclear power plant “Busher”. We discuss the reasons of ring structures formation.

Discussions on rockburst and dynamic ground support in deep mines

Abstract The paper is a summary of discussions on four topics in rockburst and dynamic ground support. Topic 1 is the mechanisms of rockburst. Rockburst events are classified into two categories in accordance with the triggering mechanisms, i.e. strain burst and fault-slip burst. Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks. Fault-slip burst is triggered by fault-slip induced seismicity. Topic 2 is prediction and forecasting of rockburst events. Prediction for a rockburst event must tell the location, timing and magnitude of the event. Forecasting could simply foresee the probability of some of the three parameters. It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies, but forecasting is possible, for example the possible locations of strain burst in an underground opening. At present, the approach using seismic monitoring and numerical modelling is a promising forecasting method. Topic 3 is preconditioning methods. The current preconditioning methods are blasting, relief-hole drilling and hydrofracturing. Defusing fault-slip seismicity is difficult and challenging but has been achieved. In very deep locations (>3000 m), the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required. Topic 4 is dynamic ground support against rockburst. Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass. The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps. Yielding props and engineered timber props are also used for dynamic support.

Probability, Causality and False Alarms using Correlations Between Strong Earthquakes and NOAA High Energy Electron Bursts

A proposal for testing the feasibility of strong earthquake forecasting from space, using on board high energy particle detectors of existing NOAA polar satellites, is given. Previously, exceptional increases of particle fluxes prior to and after the largest quakes that struck the Indonesian and the Philippine areas were recently recognised utilising NOAA-15 particle telescopes. A statistically significant correlation between electron bursts of 30 – 100 keV and large seismic events was calculated in previous publications, occurring 2 – 3 hours between seismic events having M ≥ 6 and electron bursts. The 2 – 3 hour correlation supports the hypothesis that there is a physical link between ionospheric charged particle motions at around 2,000 km and seismic activities when earthquake depths are less than 200 km. Taking into account the corresponding electron drift periods and the detector energy corrections, the time interval of a possible physical interaction between high energy electrons of the inner radiation belts and the earth's crust of the future earthquake epicentre has been reduced to about 4 – 6.5 hours. A causal model is proposed for the entire process. Cross-correlation coefficients are calculated starting from the previously obtained correlations, so that a probability of earthquake forecasting corresponding to the 2 – 3 hour peak can be evaluated. Based on these results, false alarms can be reduced in an experiment where such probability is used for one year of average seismic and electron loss detections. Finally, an experiment is proposed here, which is currently feasible using ongoing NOAA satellites and USA West Coast antennas to test the forecasting.

Hazard and Risk Assessment of Large Seismic Events Owing to CO2 Injection

Water injection for disposal has been shown to be capable of inducing seismicity. CO2 injection for storage is a promising technology to mitigate greenhouse gas emissions; however, it is liable to experience many of the same induced seismicity problems as water injection if proper precautions are not taken. Here, a seismicity model is proposed which predicts the probability of a seismic event which exceeds a certain moment magnitude due to a fluid injection scenario. The seismicity model is a semi-analytical variant of the model originally proposed by Layland-Bachmann et al., 2012 such that the need for Monte Carlo simulation is avoided. This allows the model to be quicker and use less computer memory. The model avoids explicitly modelling faults as many induced events have been occurring on previously unmapped faults. The model further assumes a critically stressed crust, a worst-case scenario for seismic risk. Additionally, the model accounts for lithology differences honoring the fact that different lithologies are more likely to produce seismic events than others. An example site selection scenario is presented illustrating the utility of the model.

Mode of slip and crust–mantle interaction at oceanic transform faults

Oceanic transform faults, connecting offset mid-ocean spreading centres, rupture quasi-periodically in earthquakes up to about magnitude M 7.0 that are often preceded by foreshocks. In addition to seismic slip, a large portion of slip takes place as aseismic creep, which likely influences initiation of large earthquakes. Although oceanic transform faults are one of the major types of plate boundaries, the exact mode of slip and interaction between the seismic and aseismic motion remains unclear. Here we present a detailed model of the mode of slip at oceanic transform faults based on data acquired from a recent temporary deployment of ocean-bottom seismometers at the Blanco Transform Fault and existing regional and teleseismic observations. In the model, the crustal part of the fault is brittle and fully seismically coupled, while the fault in the mantle, shallower than the depth of the 600 °C isotherm, creeps partially and episodically. The creep activates small asperities in the mantle that produce seismic swarms. Both mantle and the crustal zones release most of the plate-motion strain during large-magnitude earthquakes. Large earthquakes appear to be preceded by a brief episode of shallow mantle creep, accompanied by seismic swarms, which explains the observation of foreshocks and shows that mantle creep likely influences initiation of large seismic events. Earthquakes in the crust and mantle at transform faults are distinct yet coupled, with seismic swarms in the mantle apparently preceding large earthquakes, according to ocean-bottom seismic monitoring of the Blanco Transform Fault.

Integration of underground mapping, petrology, and high-resolution microseismicity analysis to characterise weak geotechnical zones in deep South African gold mines

A highly-stressed shaft pillar is prone to large seismic events, falls of ground and rockbursts, which may cause injuries and loss of production, especially in weak geotechnical zones. It is thus important to identify weak geotechnical zones in order to mitigate risks. In this study, we present integrated studies (underground mapping, petrology, rock mechanics and high-resolution microseismicity analysis) to understand the different geotechnical zones in the shaft pillar of Cooke 4 mine in South Africa. The footwall of the remnant shaft pillar comprises the Upper Elsburg reef of the Mondeor Formation, while the Ventersdorp Contact Reef (VCR) of the Venterspost Formation and soft/weak lavas of the Westonaria Formation form the hangingwall. Results from underground mapping and microscopic analysis show that the shaft pillar is composed of quartzites, pebbly quartzites, argillaceous quartzites and conglomerates. Underground mapping further shows that the shaft pillar is characterized by several discontinuities, which vary from minor to macro scale fractures. Laboratory uniaxial compressive strength (UCS) tests indicate that quartzite has the strongest strength, followed by pebbly quartzite, argillaceous quartzite and lastly, conglomerate. Analysis of high-resolution acoustic emissions (AEs) clusters indicates that the majority of AEs are associated with the mining stope faces. The clusters show the formation of Ortlepp shears ahead of the stope, which is caused by the excavation-induced stress field. Microseismic data further reveal that the fracture turning-point occurs in the soft strata (weak hangingwall lavas). The integration of these datasets has allowed us to develop the fracture model for different geotechnical zones, which concurs with previous models developed for the similar underground environment (i.e., weak/soft lava hangingwall and quartzite/conglomerate footwall). This has major implications for future mining, support, production and safety.