There is growing concern about seismicity triggered by human activities, whereby small increases ... more There is growing concern about seismicity triggered by human activities, whereby small increases in stress bring tectonically loaded faults to failure. Examples of such activities include mining, impoundment of water, stimulation of geothermal fields, extraction of hydrocarbons and water, and the injection of water, CO2 and methane into subsurface reservoirs1. In the absence of sufficient information to understand and control the processes that trigger earthquakes, authorities have set up empirical regulatory monitoring-based frameworks with varying degrees of success2,3. Field experiments in the early 1970s at the Rangely, Colorado (USA) oil field4 suggested that seismicity might be turned on or off by cycling subsurface fluid pressure above or below a threshold. Here we report the development, testing and implementation of a multidisciplinary methodology for managing triggered seismicity using comprehensive and detailed information about the subsurface to calibrate geomechanical and earthquake source physics models. We then validate these models by comparing their predictions to subsequent observations made after calibration. We use our approach in the Val d'Agri oil field in seismically active southern Italy, demonstrating the successful management of triggered seismicity using a process-based method applied to a producing hydrocarbon field. Applying our approach elsewhere could help to manage and mitigate triggered seismicity.
Histories of vertical crustal motions at convergent margins offer fundamental insights into the r... more Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and (230)Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4-40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate t...
A four-component quartz tube strainmeter with capacitance transducers has been installed in a sur... more A four-component quartz tube strainmeter with capacitance transducers has been installed in a surface site on the small coral island of Tongatapu in Tonga. Analysis of 30 days of data indicates that temperature and pressure effects are small, but that rainfall may have a significant effect. Semidiurnal lunar tidal strains with peak-to-peak amplitudes larger than 1.0 × 10−7 are observed on all components, as are semidiurnal areal strains of 2.0 × 10−7 and higher. These results are not completely explained by conventional ocean loading models, but a simple argument shows that these strains are consistent with recent reports of anomalously large tidal amplitudes in well levels on coral island aquifers. The tidal strains exhibit a “saw-tooth” shape, for the strain curve approaches compressional minima with steeper slopes than compressional maxima. This indicates a nonlinear response to the lunar driving foce, which apparently is due to loading by nonlinear tides in a lagoon near the str...
Bulletin of the Seismological Society of America, Jun 1, 1985
Abstract Using observations from 28 seismograph stations in southern Alaska, we have used the JHD... more Abstract Using observations from 28 seismograph stations in southern Alaska, we have used the JHD method to relocate 341 well-recorded events with focal depths beneath about 40 km which occurred between 56.4 N and 60.5 N, and between 151.6 W and 156.5 W. ...
Bulletin of the Seismological Society of America, Feb 1, 1982
... 208 LAWTON, FROHLICH, PULPAN, AND LATHAM ... presence of inclined seismic zones also produces... more ... 208 LAWTON, FROHLICH, PULPAN, AND LATHAM ... presence of inclined seismic zones also produces dramatic effects on phase arrival times at teleseismic stations (eg, Cleary, 1967; Douglas, 1967; Davies and McKenzie, 1969; Davies and Julian, 1972; Jacob, 1972; Sleep ...
We propose simple graphical methods for evaluating whether a set of direction vectors are cluster... more We propose simple graphical methods for evaluating whether a set of direction vectors are clustered with respect to particular directions, axes, or planes. As examples of these techniques, we present data concerning the relationship between: (1) aftershock/initial event geometry and nodal planes of focal mechanisms; (2) aftershock/initial event geometry and the plane of the Wadati-Benioff zone; and (3) B axes of focal mechanisms and the plane of the Wadati-Benioff zone.
We have undertaken a simplified calculation of orbital forcing back through the Cretaceous to the... more We have undertaken a simplified calculation of orbital forcing back through the Cretaceous to the Late to Middle Jurassic from 65 to 190 Ma. So long as the Earth has a continental ice volume, orbital forcing will impose a 400-ky periodicity upon glacioeustasy and thereby on fourth-order sequence stratigraphy cycles. Similarly, third-order cycles were defined by orbital forcing of 2.4 ± 0.4 my (predominately 2.0- and 2.8-my cycles). These concepts greatly simplified the task of unraveling sequence stratigraphy. Our sea-level calculations are comparable with stratigraphic observations and the results are consistent with a persistent continental ice volume throughout the Late to Middle Jurassic and Cretaceous. In general, they compare well with the Arabian Plate Maximum Flooding Surfaces and the Cretaceous and Jurassic stage boundaries, within the limits of the recognized stratigraphic time scales. We used simple Parametric Forward Models (PFMs) for modeling changes in sea level, subsi...
An earthquake occurred at approximately 2338 UTC on July 20, 1991 (1838 CDT), in the vicinity of ... more An earthquake occurred at approximately 2338 UTC on July 20, 1991 (1838 CDT), in the vicinity of Falls City, Texas (Fig. 1), a small community situated about 67 km southeast of San Antonio. Using observations from ALQ, ATX, GOL, TUL and VVO, the NEIS reported a preliminary location of 29.0N 98.1W, and a body wave magnitude (mb) of 3.6, with no instrumentally measured focal depth. ATX (Austin, Texas) was the closest station. To determine the extent and intensity of the felt area of this earthquake, we published an earthquake questionnaire in the Karnes City Citation, the local newspaper, and one of us (Daniel Olson) personally interviewed people in Falls City and the surrounding area. All felt reports collected formed the basis for determining the felt area of this event (Figure 1). These reports varied from not felt, to felt and accompanied with loud noise, such as an explosion or a sonic boom. The felt area centered approximately on Falls City (29.0N, 98.0W), 11 kilometers east of the NEIS preliminary location. The felt area was oblong in shape, trending northeast-southwest, parallel to the Karnes and Wilson county line. The area of Modified Mercalli intensity IV felt reports covered 75 square km, and might have been large as 250 square km, if we include sparsely populated areas north and west of Falls City. For either 75 or 250 square km, the Nuttli et al. (1979) relation between intensity IV felt area and mb is consistent with mb of only 3.0 or less. . . .
Deep Sea Research Part B. Oceanographic Literature Review
Page 1. Bulletin of the Seismological Society of America, Vol. 75, No. 2, pp. 397-413, April 1985... more Page 1. Bulletin of the Seismological Society of America, Vol. 75, No. 2, pp. 397-413, April 1985 MODEL CALCULATIONS OF REGIONAL NETWORK LOCATIONS EARTHQUAKES IN SUBDUCTION ZONES BY JAMES P. MCLAREN* AND CLIFF FROHLICH FOR ...
ABSTRACT We investigate possible links between seismicity and fluid injection in the Williston ba... more ABSTRACT We investigate possible links between seismicity and fluid injection in the Williston basin in the north-central United States, focusing on the region around the Bakken formation unconventional hydrocarbon play. Here, we show earthquakes are rarer near injection wells in the Williston basin than in the Fort Worth basin of Texas or in central Oklahoma. To identify earthquakes, we analyze seismograms collected by Earth-Scope USArray temporary stations, deployed on a grid with 70 km spacing. During the September 2008 May 2011 study period, we identified only nine regional earthquakes; of these only three were situated near injection wells. The reason why Williston basin earthquakes are so scarce is unclear. In both the Bakken and Barnett Shale play regions, injection volumes increased significantly in late 2007, and both areas have very low levels of natural seismicity. Oklahoma has experienced much higher rates of apparently induced seismicity than either region, possibly because injection volumes are higher in some wells in Oklahoma.
Online Material: Figures showing broadband station locations, waveform fit, S ‐wave velocity mode... more Online Material: Figures showing broadband station locations, waveform fit, S ‐wave velocity models, and Love‐wave fundamental mode velocities. The vast majority of earthquakes with focal depths exceeding 60 km are associated with convergent plate boundaries (Fig. 1), including a few in relict subduction zones (e.g., beneath southern Spain) and others along current or former plate boundaries presently undergoing continental convergence (Hindu Kush, Greater Tethyan Himalayas, Romania) (Zhu and Helmberger, 1996; Chen and Yang, 2004; Frohlich, 2006; Monsalve et al. , 2006). The remaining deeper, rare events within continental interiors are of special interest because their focal depths provide information about the strength and rheology of the crust and upper mantle. Figure 1. Global and regional context of the 21 September 2013 deep earthquakes. (a) Global map: The red circles are selected earthquakes with depths >60 km occurring 1977–2014, as reported by the Global Central Moment Tensor project (Ekstrom et al. , 2012). The selected earthquakes have compensated linear vector dipole components of 0.20 or less and relative error E REL<0.15; thus, they should have relatively reliable focal depths (Frohlich and Davis, 1999). (b) U.S. map: The white circles are selected deep events reported by regional networks in the western United States (Zandt and Richins, 1979; Walter, 1986; Wahlstrom, 1993; Frohlich, 2006). The red circle indicates the 21 September 2013 Wyoming earthquakes. There has been a controversy concerning whether earthquakes can occur only within the crust or also within the upper mantle. Within both regions, the strength decreases as temperature increases and thus decreases rapidly with depth. However, because crustal and mantle composition differ, the strength in the uppermost mantle exceeds the strength at the base of the crust, and it is plausible that earthquakes can …
There is growing concern about seismicity triggered by human activities, whereby small increases ... more There is growing concern about seismicity triggered by human activities, whereby small increases in stress bring tectonically loaded faults to failure. Examples of such activities include mining, impoundment of water, stimulation of geothermal fields, extraction of hydrocarbons and water, and the injection of water, CO2 and methane into subsurface reservoirs1. In the absence of sufficient information to understand and control the processes that trigger earthquakes, authorities have set up empirical regulatory monitoring-based frameworks with varying degrees of success2,3. Field experiments in the early 1970s at the Rangely, Colorado (USA) oil field4 suggested that seismicity might be turned on or off by cycling subsurface fluid pressure above or below a threshold. Here we report the development, testing and implementation of a multidisciplinary methodology for managing triggered seismicity using comprehensive and detailed information about the subsurface to calibrate geomechanical and earthquake source physics models. We then validate these models by comparing their predictions to subsequent observations made after calibration. We use our approach in the Val d'Agri oil field in seismically active southern Italy, demonstrating the successful management of triggered seismicity using a process-based method applied to a producing hydrocarbon field. Applying our approach elsewhere could help to manage and mitigate triggered seismicity.
Histories of vertical crustal motions at convergent margins offer fundamental insights into the r... more Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and (230)Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4-40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate t...
A four-component quartz tube strainmeter with capacitance transducers has been installed in a sur... more A four-component quartz tube strainmeter with capacitance transducers has been installed in a surface site on the small coral island of Tongatapu in Tonga. Analysis of 30 days of data indicates that temperature and pressure effects are small, but that rainfall may have a significant effect. Semidiurnal lunar tidal strains with peak-to-peak amplitudes larger than 1.0 × 10−7 are observed on all components, as are semidiurnal areal strains of 2.0 × 10−7 and higher. These results are not completely explained by conventional ocean loading models, but a simple argument shows that these strains are consistent with recent reports of anomalously large tidal amplitudes in well levels on coral island aquifers. The tidal strains exhibit a “saw-tooth” shape, for the strain curve approaches compressional minima with steeper slopes than compressional maxima. This indicates a nonlinear response to the lunar driving foce, which apparently is due to loading by nonlinear tides in a lagoon near the str...
Bulletin of the Seismological Society of America, Jun 1, 1985
Abstract Using observations from 28 seismograph stations in southern Alaska, we have used the JHD... more Abstract Using observations from 28 seismograph stations in southern Alaska, we have used the JHD method to relocate 341 well-recorded events with focal depths beneath about 40 km which occurred between 56.4 N and 60.5 N, and between 151.6 W and 156.5 W. ...
Bulletin of the Seismological Society of America, Feb 1, 1982
... 208 LAWTON, FROHLICH, PULPAN, AND LATHAM ... presence of inclined seismic zones also produces... more ... 208 LAWTON, FROHLICH, PULPAN, AND LATHAM ... presence of inclined seismic zones also produces dramatic effects on phase arrival times at teleseismic stations (eg, Cleary, 1967; Douglas, 1967; Davies and McKenzie, 1969; Davies and Julian, 1972; Jacob, 1972; Sleep ...
We propose simple graphical methods for evaluating whether a set of direction vectors are cluster... more We propose simple graphical methods for evaluating whether a set of direction vectors are clustered with respect to particular directions, axes, or planes. As examples of these techniques, we present data concerning the relationship between: (1) aftershock/initial event geometry and nodal planes of focal mechanisms; (2) aftershock/initial event geometry and the plane of the Wadati-Benioff zone; and (3) B axes of focal mechanisms and the plane of the Wadati-Benioff zone.
We have undertaken a simplified calculation of orbital forcing back through the Cretaceous to the... more We have undertaken a simplified calculation of orbital forcing back through the Cretaceous to the Late to Middle Jurassic from 65 to 190 Ma. So long as the Earth has a continental ice volume, orbital forcing will impose a 400-ky periodicity upon glacioeustasy and thereby on fourth-order sequence stratigraphy cycles. Similarly, third-order cycles were defined by orbital forcing of 2.4 ± 0.4 my (predominately 2.0- and 2.8-my cycles). These concepts greatly simplified the task of unraveling sequence stratigraphy. Our sea-level calculations are comparable with stratigraphic observations and the results are consistent with a persistent continental ice volume throughout the Late to Middle Jurassic and Cretaceous. In general, they compare well with the Arabian Plate Maximum Flooding Surfaces and the Cretaceous and Jurassic stage boundaries, within the limits of the recognized stratigraphic time scales. We used simple Parametric Forward Models (PFMs) for modeling changes in sea level, subsi...
An earthquake occurred at approximately 2338 UTC on July 20, 1991 (1838 CDT), in the vicinity of ... more An earthquake occurred at approximately 2338 UTC on July 20, 1991 (1838 CDT), in the vicinity of Falls City, Texas (Fig. 1), a small community situated about 67 km southeast of San Antonio. Using observations from ALQ, ATX, GOL, TUL and VVO, the NEIS reported a preliminary location of 29.0N 98.1W, and a body wave magnitude (mb) of 3.6, with no instrumentally measured focal depth. ATX (Austin, Texas) was the closest station. To determine the extent and intensity of the felt area of this earthquake, we published an earthquake questionnaire in the Karnes City Citation, the local newspaper, and one of us (Daniel Olson) personally interviewed people in Falls City and the surrounding area. All felt reports collected formed the basis for determining the felt area of this event (Figure 1). These reports varied from not felt, to felt and accompanied with loud noise, such as an explosion or a sonic boom. The felt area centered approximately on Falls City (29.0N, 98.0W), 11 kilometers east of the NEIS preliminary location. The felt area was oblong in shape, trending northeast-southwest, parallel to the Karnes and Wilson county line. The area of Modified Mercalli intensity IV felt reports covered 75 square km, and might have been large as 250 square km, if we include sparsely populated areas north and west of Falls City. For either 75 or 250 square km, the Nuttli et al. (1979) relation between intensity IV felt area and mb is consistent with mb of only 3.0 or less. . . .
Deep Sea Research Part B. Oceanographic Literature Review
Page 1. Bulletin of the Seismological Society of America, Vol. 75, No. 2, pp. 397-413, April 1985... more Page 1. Bulletin of the Seismological Society of America, Vol. 75, No. 2, pp. 397-413, April 1985 MODEL CALCULATIONS OF REGIONAL NETWORK LOCATIONS EARTHQUAKES IN SUBDUCTION ZONES BY JAMES P. MCLAREN* AND CLIFF FROHLICH FOR ...
ABSTRACT We investigate possible links between seismicity and fluid injection in the Williston ba... more ABSTRACT We investigate possible links between seismicity and fluid injection in the Williston basin in the north-central United States, focusing on the region around the Bakken formation unconventional hydrocarbon play. Here, we show earthquakes are rarer near injection wells in the Williston basin than in the Fort Worth basin of Texas or in central Oklahoma. To identify earthquakes, we analyze seismograms collected by Earth-Scope USArray temporary stations, deployed on a grid with 70 km spacing. During the September 2008 May 2011 study period, we identified only nine regional earthquakes; of these only three were situated near injection wells. The reason why Williston basin earthquakes are so scarce is unclear. In both the Bakken and Barnett Shale play regions, injection volumes increased significantly in late 2007, and both areas have very low levels of natural seismicity. Oklahoma has experienced much higher rates of apparently induced seismicity than either region, possibly because injection volumes are higher in some wells in Oklahoma.
Online Material: Figures showing broadband station locations, waveform fit, S ‐wave velocity mode... more Online Material: Figures showing broadband station locations, waveform fit, S ‐wave velocity models, and Love‐wave fundamental mode velocities. The vast majority of earthquakes with focal depths exceeding 60 km are associated with convergent plate boundaries (Fig. 1), including a few in relict subduction zones (e.g., beneath southern Spain) and others along current or former plate boundaries presently undergoing continental convergence (Hindu Kush, Greater Tethyan Himalayas, Romania) (Zhu and Helmberger, 1996; Chen and Yang, 2004; Frohlich, 2006; Monsalve et al. , 2006). The remaining deeper, rare events within continental interiors are of special interest because their focal depths provide information about the strength and rheology of the crust and upper mantle. Figure 1. Global and regional context of the 21 September 2013 deep earthquakes. (a) Global map: The red circles are selected earthquakes with depths >60 km occurring 1977–2014, as reported by the Global Central Moment Tensor project (Ekstrom et al. , 2012). The selected earthquakes have compensated linear vector dipole components of 0.20 or less and relative error E REL<0.15; thus, they should have relatively reliable focal depths (Frohlich and Davis, 1999). (b) U.S. map: The white circles are selected deep events reported by regional networks in the western United States (Zandt and Richins, 1979; Walter, 1986; Wahlstrom, 1993; Frohlich, 2006). The red circle indicates the 21 September 2013 Wyoming earthquakes. There has been a controversy concerning whether earthquakes can occur only within the crust or also within the upper mantle. Within both regions, the strength decreases as temperature increases and thus decreases rapidly with depth. However, because crustal and mantle composition differ, the strength in the uppermost mantle exceeds the strength at the base of the crust, and it is plausible that earthquakes can …
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