Global review of human-induced earthquakes

Induced seismicity and hydraulic fracturing for the recovery of hydrocarbons

We compile published examples of induced earthquakes that have occurred since 1929 that have magnitudes equal to or greater than 1.0. Of the 198 possible examples, magnitudes range up to 7.9. The potential causes and magnitudes are (a) mining (M 1.6e5.6); (b) oil and gas field depletion (M 1.0e7.3); (c) water injection for secondary oil recovery (M 1.9e5.1); (d) reservoir impoundment (M 2.0e7.9); (e) waste disposal (M 2.0e5.3); (f) academic research boreholes investigating induced seismicity and stress (M 2.8e3.1); (g) solution mining (M 1.0e5.2); (h) geothermal operations (M 1.0e4.6) and (i) hydraulic fracturing for recovery of gas and oil from low-permeability sedimentary rocks (M 1.0e3.8). Reactivation of faults and resultant seismicity occurs due to a reduction in effective stress on fault planes. Hydraulic fracturing operations can trigger seismicity because it can cause an increase in the fluid pressure in a fault zone. Based upon the research compiled here we propose that this could occur by three mechanisms. Firstly, fracturing fluid or displaced pore fluid could enter the fault. Secondly, there may be direct connection with the hydraulic fractures and a fluid pressure pulse could be transmitted to the fault. Lastly, due to poroelastic properties of rock, deformation or ‘inflation’ due to hydraulic fracturing could increase fluid pressure in the fault or in fractures connected to the fault. The following pathways for fluid or a fluid pressure pulse are proposed: (a) directly from the wellbore; (b) through new, stimulated hydraulic fractures; (c) through pre-existing fractures and minor faults; or (d) through the pore network of permeable beds or along bedding planes. The reactivated fault could be intersected by the wellbore or it could be 10s to 100s of metres from it. We propose these mechanisms have been responsible for the three known examples of felt seismicity that are probably induced by hydraulic fracturing. These are in the USA, Canada and the UK. The largest such earthquake was M 3.8 and was in the Horn River Basin, Canada. To date, hydraulic fracturing has been a relatively benign mechanism compared to other anthropogenic triggers, probably because of the low volumes of fluid and short pumping times used in hydraulic fracturing operations. These data and analysis should help provide useful context and inform the current debate surrounding hydraulic fracturing technology.

/pdf/marine-and-petroleum-geology-we3xg7lplu.pdf

Marine and Petroleum Geology

Anthropogenic processes, natural hazards, and interactions in a multi-hazard framework

The Anthropocene is a major new concept in the Earth sciences and this book examines the effects on geomorphology within this period. Drawing examples from many different global environments, this comprehensive volume demonstrates that human impact on landforms and land-forming processes is profound, due to various driving forces, including: use of fire; extinction of fauna; development of agriculture, urbanisation, and globalisation; and new methods of harnessing energy. The book explores the ways in which future climate change due to anthropogenic causes may further magnify effects on geomorphology, with respect to future hazards such as floods and landslides, the state of the cryosphere, and sea level. The book concludes with a consideration of the ways in which landforms are now being managed and protected. Covering all major aspects of geomorphology, this book is ideal for undergraduate and graduate students studying geomorphology, environmental science and physical geography, and for all researchers of geomorphology.

Geomorphology in the Anthropocene

Over the last 25 years mining-induced seismicity in the Ruhr area has continuously been monitored by the Ruhr-University Bochum. About 1,000 seismic events with local magnitudes between 0.7 ≤ ML ≤ 3.3 are located every year. For example, 1,336 events were located in 2006. General characteristics of induced seismicity in the entire Ruhr area are spatial and temporal correlation with mining activity and a nearly constant energy release per unit time. This suggests that induced stresses are released rapidly by many small events. The magnitude–frequency distribution follows a Gutenberg–Richter relation which is a result from combining distributions of single longwalls that themselves show large variability. A high b-value of about 2 was found indicating a lack of large magnitude events. Local analyses of single longwalls indicate that various factors such as local geology and mine layout lead to significant differences in seismicity. Stress redistribution acts very locally since differences on a small scale of some hundreds of meters are observed. A regional relation between seismic moment M0 and local magnitude ML was derived. The magnitude–frequency distribution of a single longwall in Hamm was studied in detail and shows a maximum at ML = 1.4 corresponding to an estimated characteristic source area of about 2,200 m2. Sandstone layers in the hanging or foot wall of the active longwall might fail in these characteristic events. Source mechanisms can mostly be explained by shear failure of two different types above and below the longwall. Fault plane solutions of typical events are consistent with steeply dipping fracture planes parallel to the longwall face and nearly vertical dislocation in direction towards the goaf. We also derive an empirical relation for the decay of ground velocity with epicenter distance and compare maximum observed ground velocity to local magnitude. This is of considerable public interest because about 30 events larger than ML ≥ 1.2 are felt each month by people living in the mining regions. Our relations, for example, indicate that an event in Hamm with a peak ground velocity of 6 mm/s which corresponds to a local magnitude ML between 1.7 and 2.3 is likely to be felt within about 2.3 km radius from the event.

Alpan Cete

Papers

Coal Mining Induced Seismicity in the Ruhr Area, Germany