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The low-noise environment in the Masada deep borehole (MDBI), an abandoned oil well on the western shore of the Dead Sea rift, allows the recordings of many small-magnitude earthquakes. MDBI has a 2 Hz triaxial seismometer installed at a depth of 1256 m below ground and 1516 m below sea level. We used MDBI P- and S-wave data and the general source relationship u(f)=u(0)e−(πft/Q)/[1+(f/f0)2y]1y, in which f0 is corner frequency and 1

A core feature of convective geothermal resource production is wellbore energy flow Q ~ ρC x T x V. E.g., for wellbore fluid of volume heat capacity ρC ~ 4.3MJ/m3∙oC, temperature T ~ 230oC, and volumetric flow V ~ 50L/s, wellbore heat energy production is Q~ 50MWth ~ 5MWe. Wellbore fluid flow V =2πr0φv0l for open wellbore length l is given in turn by the spatially variable product crustal porosity times crustal fluid velocity v ≡ φv0 at the wellbore radius r0. For a geothermal wellbore to be productive (nominal Q ~ 5MWe), locally variable bulk inflow rates v = φv0 across crustal volumes of dimension l must be adequate to sustain high wellbore flows (nominal V ~ 50L/s). Wide-ranging crustal well productivity statistics show that few crustal wells flow at these rates. This is not surprising as local bulk flow ~ 10-2 m/s needed for production wellbores is decades greater than ambient bulk fluid flow ~ 10-8-10-7m/s characteristic of natural convective geothermal systems. Such rare high flow locales must be found. While existing crustal surveys generally fix resource temperatures T with nominal 500m spatial resolution, as yet no survey technique provides data to locate production-grade flow rates at nominal l ~ 50m spatial resolution. In consequence, many costly unproductive wells are drilled before sites of productive local geothermal fluid bulk flow v = φv0 ~ 10-2 m/s are located. A seismic survey methodology sensitive to crustal flow v = φv0 at l ~25m resolution has evolved from multi-channel seismic reflection technology applied to the production of shale hydrocarbons. The field-proven seismic flow-imaging methodology can be adapted from sedimentary terrains to volcanic terrains through appropriate seismic refraction means for generating effective seismic velocity models for convective geothermal flow volumes. Numerical simulation for characteristic ambient crustal heterogeneous flow distributions v = φv0 at l ~50m resolution shows that travel-time data for seismic source energy refracted from deep geothermal wellbores to surface seismic sensor arrays can replicate the multi-channel seismic flow-imaging capability demonstrated for shale formations. Multi-channel seismic reservoir flow monitor detection and mapping of flow-induced seismic emissions in shale formations can be adapted to achieve similar mapping of convective geothermal flow system structures with v = φv0 ~ 10-2m/s at nominal l ~ 50m resolution. Such seismic emission flow structure maps can greatly reduce the uncertainty and hence the cost of drilling effective production wells at brownfield sites and assessment/development wells at greenfield sites

A better understanding of the Dead Sea basin (DSB) tectonics and hazards can be achieved through high-sensitivity observations of its seismic activity. Accordingly, we have taken advantage of the Masada deep borehole (MDBI), an abandoned oil well on the western shore of the Dead Sea rift, to install a seismometer at 1516 m below sea level—a 2 Hz three-component seismometer. The MDBI station is near the east Masada fault, part of the western boundary fault of the DSB. Seismological measurements conducted at these depths can provide more information than possible with surface observations—in this case, recording 1491 high-quality seismograms as compared to 103 by the local national network. The MDBI seismograms also have significantly higher signal-to-noise ratio than the on-surface observations of nearby Israel Seismic Network (ISN) stations. This lowers the detection threshold down to well below M = 0 on the ISN scale. Many of these earthquakes, sometimes occurring in clusters, take place almost under MDBI, at depths of 10–25 km. Using cross-correlation techniques, we found several sequences of earthquake clusters underneath both the station and along the Dead Sea fault (DSF). The b-value obtained by the frequency–magnitude relationship of these events is somewhat higher than the value for the DSF area taken as a whole.

Given its intense seismic activity and damaging earthquake generation potential, the western part of the North Anatolian Fault constitutes a serious natural hazard. As a result, the fault is monitored with a broad range of seismological and geodetic instrumentation making it a natural laboratory environment for scientific studies. One of the long-term projects in this region is GONAF (Geophysical Borehole Observatory at the North Anatolian Fault) which is the first borehole seismometer network project in Turkey. GONAF is a joint research project that started in 2011 as joint initiative of the Turkish Ministry of Interior, Disaster and Emergency Management Presidency AFAD and GFZ and the German Research Center for Geoscience Helmholtz Center Potsdam. The aim of GONAF is to detect, examine, and monitor the microseismic activity in the region and to observe the physical processes before, during and after a large Marmara earthquake (M > 7.0) that is expected to rupture the western part of the North Anatolian Fault, below the Marmara Sea along the Princes Islands segment or even further to the west. For this purpose, the permanent GONAF observatory was established consisting of 7 borehole seismometer arrays installed down to a depth of 300 m. In this paper, we report on regional stress changes in the western part of the North Anatolian Fault Zone (NAFZ) using instrumental data and the Coulomb stress method. We also present preliminary results of the observation and evaluation of microseismic activity obtained from the GONAF observatory. For the automatic evaluation of real-time data, Seiscomp3, RTQUAKE, and Earthworm Softwares were used. Within the scope of automatic earthquake detection studies, between March, 2016 and November, 2017, a total of 2568 earthquakes were detected using the RTQUAKE software. Of these, 1459 could be analyzed. While the magnitude of the analyzed earthquakes varies between 0.8 and 4.2, the depth of these events ranges from 2 to 30 km.

We describe the design and implementation of a traffic light system (TLS) created for the stimulation phase of a 6.1-km-deep geothermal well in the Helsinki area, Finland. Because of the lack of local seismic data to calibrate the TLS, the TLS thresholds have been proposed on the basis of two parameters: acceptable ground motion levels and probabilities to reach these levels, which were then used to establish TLS magnitudes. A peak ground velocity (PGV) of 1 mm/s associated with a ML ≥ 1 event, or a ML ≥ 1.2 event alone, triggered an Amber alert. A PGV of 7.5 mm/s associated with a ML ≥ 2.1 event triggered a Red alert, where ML was a local “Helsinki” magnitude. Specific thresholds based on PGV and peak ground acceleration were gathered for critical infrastructure sites and related to earthquake magnitudes in a probabilistic way. The implementation of the TLS during the stimulation showed that the selected thresholds were reasonably conservative. Some of the Amber events were reportedly felt or heard, but the public opinion remained very favourable to the project. Measured ground motions were too low to have any impact on the built environment and the stimulation was able to proceed without being impaired by the occurrence of a Red event. Seismic data acquired during the stimulation and lessons learnt are presented and used to revisit the TLS thresholds for potential future stimulations.

In interest of accurately modelling wellbore production in convective geothermal systems, we draw attention to two approaches to numerical simulation of crustal fluid flow. The historical ‘’strong’’ approach simulates the fluid mass conservation condition on a localised finite difference mesh approximation to poroelastic continua. The more flexible ‘’weak’’ approach globally enforces fluid mass conservation by in effect integrating over all numerical mesh cells. Strong formulation crustal flow simulation emerged from numerical simulations of mathematically tractable conductive heat flow in media typified by normally-distributed/spatially-uncorrelated thermal property distributions. Strong formulation numerical stability problems quickly intrude, however, when confronted with the lognormally-distributed/spatially-correlated crustal permeability distributions that pervade the ambient crust. Weak flow conservation solver formulations accurately handle abrupt wide-ranging crustal permeability spatial fluctuations arising from these crustal permeability structures. We use two Matlab-based weak formulation flow simulation schemes to model wellbore-centric production fluid connectivity within large-scale spatially erratic convective geothermal flow structures described by the empirical poroperm relation k(x,y,z) ~ exp(αφ(x,y,z)) acting over cm-to-km scale lengths. Through weak formulation reservoir flow modelling of convective geothermal systems, the advancing ability to support large-scale crustal flow structure models with multi-channel surface seismic data acquisition/processing can guide geothermal field exploration and developmental drilling via feedback loops between crustal flow imaging data and accurate wellbore production modelling data.

Earthquakes are frequently accompanied by public reports of audible low-frequency noises. In 2018, public reports of booms or thunder-like noises were linked to induced earthquakes during an Engineered Geothermal System project in the Helsinki Metropolitan area. In response, two microphone arrays were deployed to record and study these acoustic signals while stimulation at the drill site continued. During the 11 day deployment, we find 39 earthquakes accompanied by possible atmospheric acoustic signals. Moment magnitudes of these events ranged from $$-0.07$$ - 0.07 to 1.87 with located depths of 4.8–6.5 km. Analysis of the largest event revealed a broadband frequency content, including in the audible range, and high apparent velocities across the arrays. We conclude that the audible noises were generated by local ground reverberation during the arrival of seismic body waves. The inclusion of acoustic monitoring at future geothermal development projects will be beneficial for studying seismic-to-acoustic coupling during sequences of induced earthquakes.

A seismic network was installed in Helsinki, Finland to monitor the response to an ∼6-kilometer-deep geothermal stimulation experiment in 2018. We present initial results of multiple induced earthquake seismogram and ambient wavefield analyses. The used data are from parts of the borehole network deployed by the operating St1 Deep Heat Company, from surface broadband sensors and 100 geophones installed by the Institute of Seismology, University of Helsinki, and from Finnish National Seismic Network stations. Records collected in the urban environment contain many signals associated with anthropogenic activity. This results in time- and frequency-dependent variations of the signal-to-noise ratio of earthquake records from a 260-meter-deep borehole sensor compared to the combined signals of 24 collocated surface array sensors. Manual relocations of ∼500 events indicate three distinct zones of induced earthquake activity that are consistent with the three clusters of seismicity identified by the company. The fault-plane solutions of 14 selected ML 0.6–1.8 events indicate a dominant reverse-faulting style, and the associated SH radiation patterns appear to control the first-order features of the macroseismic report distribution. Beamforming of earthquake data from six arrays suggests heterogeneous medium properties, in particular between the injection site and two arrays to the west and southwest. Ambient-noise cross-correlation functions reconstruct regional surface-wave propagation and path-dependent body-wave propagation. A 1D inversion of the weakly dispersive surface waves reveals average shear-wave velocities around 3.3 km/s below 20 m depth. Consistent features observed in relative velocity change time series and in temporal variations of a proxy for wavefield partitioning likely reflect the medium response to the stimulation. The resolution properties of the obtained data can inform future monitoring strategies and network designs around natural laboratories.

Fracture seismic is the method for recording and analyzing passive seismic data for mapping the fractures in the subsurface. Fracture seismic is able to map the fractures because of two types of mechanical actions in the fractures. First, in cohesive rock, fractures can emit short duration energy pulses when growing at their tips through opening and shearing. The industrial practice of recording and analyzing these short duration events is commonly called micro-seismic. Second, coupled rock&ndash, fracture&ndash, fluid interactions take place during earth deformations and this generates signals unique to the fracture&rsquo, s physical characteristics. This signal appears as harmonic resonance of the entire, fluid-filled fracture. These signals can be initiated by both external and internal changes in local pressure, e.g., a passing seismic wave, tectonic deformations, and injection during a hydraulic well treatment. Fracture seismic is used to map the location, spatial extent, and physical characteristics of fractures. The strongest fracture seismic signals come from connected fluid-pathways. Fracture seismic observations recorded before, during, and after hydraulic stimulations show that such treatments primarily open pre-existing fractures and weak zones in the rocks. Time-lapse fracture seismic methods map the flow of fluids in the rocks and reveal how the reservoir connectivity changes over time. We present examples that support these findings and suggest that the fracture seismic method should become an important exploration, reservoir management, production, and civil safety tool for the subsurface energy industry.

Near-realtime seismic monitoring of fluid injection allowed management of induced seismicity during a soft stimulation of a 6.1-km-deep geothermal well near Helsinki, Finland. A total of 18,160 m3 of fresh water were pumped into crystalline rocks over 49 days in June-July 2018. Well-head stimulation pressures were varied between 60–90 MPa and flow rates between 400–800 l/min. Seismic monitoring was performed with a 24-station borehole seismometer network, including a 2.2–2.6 km deep 12-level array of 3 component sensors. Using near-realtime acquisition and analysis of induced-earthquake rates, locations, magnitudes, and evolution of radiated seismic versus hydraulic energy, pumping was either stopped or varied. This procedure avoided the nucleation of a regulator mandated maximum magnitude M 2.1 induced earthquake. These results are consistent with a crack-stability physics approach to controlling stimulation induced seismicity in geothermal projects.

Using Fracture Seismic methods to map fluid-conducting fracture zones makes it important to understand fracture connectivity over distances greater 10&ndash, 20 m in the Earth&rsquo, s upper crust. The principles required for this understanding are developed here from the observations that (1) the spatial variations in crustal porosity are commonly associated with spatial variations in the magnitude of the natural logarithm of crustal permeability, and (2) many parameters, including permeability. have a scale-invariant power law distribution in the crust. The first observation means that crustal permeability has a lognormal distribution that can be described as k &asymp, k0 exp (&alpha, (&Phi, &Phi, 0)), where &alpha, is the ratio of the standard deviation of ln permeability from its mean to the standard deviation of porosity from its mean. The scale invariance of permeability indicates that &alpha, 0= 3 to 4 and that the natural log of permeability has a 1/k pink noise spatial distribution. Combined, these conclusions mean that channelized flow in the upper crust is expected as the distance traversed by flow increases. Locating the most permeable channels using Seismic Fracture methods, while filling in the less permeable parts of the modeled volume with the correct pink noise spatial distribution of permeability, will produce much more realistic models of subsurface flow.

The Marmara section of the North Anatolian Fault Zone (NAFZ) runs under water and is located less than 20 km from the 15-million-person population center of Istanbul in its eastern portion. Based on historical seismicity data, recurrence times forecast an impending magnitude M>7 earthquake for this region. The permanent GONAF (Geophysical Observatory at the North Anatolian Fault) has been installed around this section to help capture the seismic and strain activity preceding, during, and after such an anticipated event.

International audience; General awareness of induced seismicity and gas leakage related to energy reservoir exploitation has been on the rise for several years (McGarr, 2002; Davies et al., 2013). This includes events from short-term fluid injection for reservoir simulation (Giardini, 2009; Atkinson, 2016), Long term hydrocarbon extraction (Van Thienen-Visser and Breuness, 2015), under¬ground storage of natural gas (Cesca et al., 2014), waster water (Ellsworth, 2013), and carbon dioxide (Zoback and Gorelick, 2012). High rates of felt induced events in previously quiet areas are now considered critical for public safety and social licence to operate (Petersen et al, 2016). Concerns about con¬tamination of ground water and climate effects have followed suit (Darrah et al., 2014; Davies et al., 2014). Prominent injection-induced seismicity that raised concerns are: the Preese Hall-1 frack-related M2.3 in the United King¬dom (de Pater and Baisch, 2011; Clark et al., 2014); an M~3.4 during the Basel, Switzerland, Geothermal project (Häring et al., 2008; Giardini, 2009), increased central-US water-disposal M>3 earthquakes (e.g. Ellsworth, 2013), and M~4 fracking-in¬duced events in Canada (Atkinson et al., 2016). In the case of gas leakage owing to loss of well integrity, industry long-run estimates range between a few per cent to as much as 50% (Burfatto et al., 2003). For non-conventional resource wells drilled since 2009 in Pennsylvania, well-inspec¬tion records suggest that as many as 40% have integrity issues (Davies et al. 2014; Ingraffea et al., 2014) and China (Lei et al., 2017). The proliferation of microearthquakes many times foreshad¬ows damaging ones and changes in well integrity. Substantial progress has been made in cost-effective, specialized seismic networks that can address these issues (e.g., Van der Baan et al., 2013). We describe these over a ~ 5 x 5 km reservoir in a ~10 x 10 km lease. As the optimal best practice, we suggest the monitoring scheme be integrated into a reservoir-management plan using Seismic Emission Tomography (SET; e.g. Sicking et al., 2017). In addition to adding value for fracture characterization and production management, only a portion of a permanent SET net is needed for regulatory compliance.

Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7–35 Hz) have been recorded on shallow borehole seismometers installed within 20 m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60–200 m with a 10–40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

We use Matlab 3D finite element fluid flow/transport modelling to simulate localized wellbore temperature events of order 0.05-0.1oC logged in Fennoscandia basement rock at ~ 1.5km depths. The temperature events are approximated as steady-state heat transport due to fluid draining from the crust into the wellbore via naturally occurring fracture-connectivity structures. Flow simulation is based on the empirics of spatially-correlated fracture-connectivity fluid flow widely attested by well-log, well-core, and well-production data. Matching model wellbore-centric radial temperature profiles to a 2D analytic expression for steady-state radial heat transport with Peclet number Pe ≡ r0φv0/D (r0 = wellbore radius, v0 = Darcy velocity at r0, φ = ambient porosity, D = rock-water thermal diffusivity), gives Pe ~ 10-15 for fracture-connectivity flow intersecting the well, and Pe ~ 0 for ambient crust. Darcy flow for model Pe ~ 10 at radius ~ 10 meters from the wellbore gives permeability estimate κ ~ 0.02Darcy for flow driven by differential fluid pressure between least principal crustal stress pore pressure and hydrostatic wellbore pressure. Model temperature event flow permeability κm ~ 0.02Darcy is related to well-core ambient permeability κ ~ 1µDarcy by empirical poroperm relation κm ~ κ exp(αmφ) for φ ~ 0.01 and αm ~ 1000. Our modelling of wellbore temperature events calibrates the concept of reactivating fossilized fracture-connectivity flow for EGS permeability stimulation of basement rock.

Discriminating between a creeping and a locked status of active faults is of central relevance to characterize potential rupture scenarios of future earthquakes and the associated seismic hazard for nearby population centres. In this respect, highly similar earthquakes that repeatedly activate the same patch of an active fault portion are an important diagnostic tool to identify and possibly even quantify the amount of fault creep. Here, we present a refined hypocentre catalogue for the Marmara region in northwestern Turkey, where a magnitude M up to 7.4 earthquake is expected in the near future. Based on waveform cross-correlation for selected spatial seismicity clusters, we identify two magnitude M ∼ 2.8 repeater pairs. These repeaters were identified as being indicative of fault creep based on the selection criteria applied to the waveforms. They are located below the western part of the Marmara section of the North Anatolian Fault Zone and are the largest reported repeaters for the larger Marmara region. While the eastern portion of the Marmara seismic gap has been identified to be locked, only sparse information on the deformation status has been reported for its western part. Our findings indicate that the western Marmara section deforms aseismically to a substantial extent, which reduces the probability for this region to host a nucleation point for the pending Marmara earthquake. This is of relevance, since a nucleation of the Marmara event in the west and subsequent eastward rupture propagation towards the Istanbul metropolitan region would result in a substantially higher seismic hazard and resulting risk than if the earthquake would nucleate in the east and thus propagate westward away from the population centre Istanbul.

Since 1995 the eruption of the andesitic Soufriere Hills Volcano (SHV), Montserrat, has been studied in substantial detail. As an important contribution to this effort, the Seismic Experiment with Airgunsource-Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory (SEA-CALIPSO) experiment was devised to image the arc crust underlying Montserrat, and, if possible, the magma system at SHV using tomography and reflection seismology. Field operations were carried out in October–December 2007, with deployment of 238 seismometers on land supplementing seven volcano observatory stations, and with an array of 10 ocean-bottom seismometers deployed offshore. The RRS James Cook on NERC cruise JC19 towed a tuned airgun array plus a digital 48-channel streamer on encircling and radial tracks for 77 h about Montserrat during December 2007, firing 4414 airgun shots and yielding about 47 Gb of data. The main objecctives of the experiment were achieved. Preliminary analyses of these data published in 2010 generated images of heterogeneous high-velocity bodies representing the cores of volcanoes and subjacent intrusions, and shallow areas of low velocity on the flanks of the island that reflect volcaniclastic deposits and hydrothermal alteration. The resolution of this preliminary work did not extend beyond 5 km depth. An improved three-dimensional (3D) seismic velocity model was then obtained by inversion of 181 665 first-arrival travel times from a more-complete sampling of the dataset, yielding clear images to 7.5 km depth of a low-velocity volume that was interpreted as the magma chamber which feeds the current eruption, with an estimated volume 13 km3. Coupled thermal and seismic modelling revealed properties of the partly crystallized magma. Seismic reflection analyses aimed at imaging structures under southern Montserrat had limited success, and suggest subhorizontal layering interpreted as sills at a depth of between 6 and 19 km. Seismic reflection profiles collected offshore reveal deep fans of volcaniclastic debris and fault offsets, leading to new tectonic interpretations. This chapter presents the project goals and planning concepts, describes in detail the campaigns at sea and on land, summarizes the major results, and identifies the key lessons learned.

The American Association of Petroleum Geologists sponsored a Hedberg Research Conference on Enhanced Geothermal Systems in Napa, California, March 18 to 23, 2011. The workshop was attended by 67 participants from 10 different countries: United States, Australia, Austria, Canada, Colombia, Germany, Malaysia, Netherlands, New Zealand, and Norway. No large energy segment grows based on skill sets possessed by one or a few individuals alone. In the case of enhanced geothermal systems (EGS, also known as “engineered GS”), this was brought home to all participants through a set of posters and presentations on national and regional programs. A presentation by Bendall et al. representing the primary industries and resource agency of South Australia was very effective in conveying how to manage communication between and facilitation among the national research groups and dedicated geothermal research centers. David Blackwell's geothermal laboratory at Southern Methodist University (SMU) in Dallas serves a similar function in the United States. They conduct the dual responsibilities of basic research on the national U.S. heat-flow database and are heavily engaged in geothermal developments related to oil and gas production throughout the Gulf Coast region and elsewhere. The International Geothermal Center (GZB) in Bochum, Germany, is yet another model, as reported by Rolf Bracke and Volker Wittig. The state of North Rhine–Westphalia is investing in a coiled tube drilling rig for use by the GZB at Hochschule Bochum. The rig will drill a deep well on the university campus and fracture the rocks between multiple lateral wellbores. The resulting geothermal field will be developed to provide overall heating for the GZB and, if possible, for the rest of the university. The GZB is also charged with educating the public about the relative risks of subsurface engineering actions. For example, the public will be able to observe the relative seismic effects …

To better understand the volcanic phenomena acting on Montserrat, the SEA-CALIPSO seismic experiment (Seismic Experiment with Airgun-source - Caribbean Andesitic Lava Island Precision Seismo-geodetic Observatory) was conducted in 2007 December with the aim of imaging the upper crust and the magmatic system feeding the active Soufriére Hills Volcano. The 3-D survey covered an area of about 50 × 40 km and involved the deployment of 247 land stations and ocean-bottom seismometers (OBSs). A subset of the data, recorded by four OBSs and four land stations on a southeast to northwest line, has been analysed, and traveltimes have been inverted to obtain a 2-D seismic velocity model through the island. Inverted phases include crustal and sediment P waves and wide-angle reflections. The resulting velocity model reveals the presence of a high velocity body (3.5-5.5 km s-1) beneath the island, with highest velocities beneath the Soufriére and Centre Hills, corresponding primarily to the cores of these volcanic edifices, built of a pile of andesite lava domes and subsequent intrusions. In the offshore region, velocities in the surficial sediment layer vary from 1.5 to 3.0 km s-1, consistent with a mainly calcareous and volcaniclastic composition. A wide-angle reflector is observed at a depth of ∼1200 m below the seabed, and appears to deepen beneath the island. The upper crust beneath this reflector has velocities of 4.0-6.0 km s-1 and is inferred to correspond to plutonic and hypabyssal rocks and sedimentary material of the old arc. The high velocity region beneath the island, extends into the crust to a depth of at least 5 km, and is believed to be caused by an intrusive complex, possibly of intermediate composition. A low velocity zone, as would be expected in the presence of an active magma chamber, was not observed perhaps due to the limited resolution beneath ∼5 km depth. Our results so far provide the first wide-angle seismic constraints on the upper crustal structure of the island to a depth of 10 km, and will help understanding the processes that drive volcanism at Montserrat and other island arc volcanoes. © 2009 The Authors Journal compilation © 2009 RAS.

Using the first dataset available from the downhole Geophysical Observatory of the North Anatolian Fault, we investigated near‐surface seismic‐wave propagation on the Tuzla Peninsula, Istanbul, Turkey. We selected a dataset of 26 seismograms recorded at Tuzla at sensor depths of 0, 71, 144, 215, and 288 m. To determine near‐surface velocities and attenuation structures, the waveforms from all sensors were pairwise deconvolved and stacked. This produced low‐noise empirical Green’s functions for each borehole depth interval. From the Green’s functions, we identified reflections from the free surface and a low‐velocity layer between ∼90 and ∼140 m depth. The presence of a low‐velocity zone was also confirmed by a sonic log run in the borehole. This structure, plus high near‐surface P ‐ and S ‐wave velocities of ∼3600–4100 and ∼1800 m/s, lead to complex interference effects between upgoing and downgoing waves. As a result, the determination of quality factors ( Q ) with standard spectral ratio techniques was not possible. Instead, we forward modeled the Green’s functions in the time domain to determine effective Q values and to refine our velocity estimates. The effective Q P values for the depth intervals of 0–71, 0–144, 0–215, and 0–288 m were found to be 19, 35, 39, and 42, respectively. For the S waves, we obtained an effective Q S of 20 in the depth interval of 0–288 m. Considering the assumptions made in our modeling approach, it is evident that these effective quality factors are biased by impedance contrasts between our observation points. Our results show that, even after correcting for a free‐surface factor of 2, the motion at the surface was found to be 1.7 times greater than that at 71 m depth. Our efforts also illustrate some of the difficulties of dealing with site effects in a strongly heterogeneous subsurface. Online Material: Plots of resistivity and caliper logs and the spectra of all 26 events.

This essay offers a selective study of the RSC's work on the plays of Shakespeare's contemporaries from 1960 to 2011, focusing on key productions within that period. Placing early productions in the theatrical and social contexts of the 1960s, it goes on to assess the impact of the RSC's investment in smaller venues such as The Other Place. From 1986, the RSC's exploration of this repertoire was largely confined to the Swan Theatre, a much-loved auditorium that nevertheless presents considerable challenges to practitioners, as this essay explores. The future prospects for Shakespeare's contemporaries within the RSC's repertoire are also briefly considered.

The city of Auckland (population 1.3 million) is built on and around a potentially active basaltic intraplate volcanic system, the Auckland volcanic field. This monogenetic field of around 50 small volcanoes covers an area of 360 km2 and may have been active for ca. 250 ka. Volcano monitoring can be difficult in small distributed volcanic fields such as the AVF as the next vent location is not known, and traditional techniques such as geochemical and ground deformation monitoring may therefore not be feasible as there is no obvious target for measurements. In such cases, seismic monitoring may be the only technique suitable. High levels of background (cultural) seismic noise and extremely low levels of historical seismicity make volcano monitoring particularly challenging in the AVF. Here, we report on recent attempts to improve monitoring capability in the AVF, which include the installation of downhole seismometers and a seismic refraction study to refine the velocity model used to locate earthquakes. We conclude that downhole instrumentation in a volcano-monitoring network allows better detection of local earthquakes, but note that several downhole sensors would be required for a network to realise the full benefits of downhole instrumentation. Our refinement of the general velocity model for Auckland has some effect on calculated earthquake locations and depths, and we suggest that further work on refining the velocity model and then its incorporation into the GeoNet earthquake location system could help us be better prepared for a future AVF eruption.