Research ArticleGEOPHYSICS

Discriminating between natural versus induced seismicity from long-term deformation history of intraplate faults

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Science Advances  24 Nov 2017:
Vol. 3, no. 11, e1701593
DOI: 10.1126/sciadv.1701593
  • Fig. 1 Post-2008 seismicity rate change in the CUS.

    The post-2008 seismicity has occurred both in areas that were seismically active before 2008 (for example, the Mississippi embayment) and in regions with no pre-2008 historical or instrumental seismicity (for example, FWB). The two study areas are outlined and represented in Figs. 2 and 6. Modified with permissions from Rubinstein and Mahani (13).

  • Fig. 2 Earthquakes in the FWB, north Texas.

    The map shows the main tectonic features of the basin, instrumental seismicity (1.8 > Mw > 4.0), and the geographical extent of the Barnett Shale, the main oil and gas production unit. Produced brine and wastewater associated with stimulation of unconventional reservoirs are reinjected through deep wells (that is, saltwater disposal well; crosses in figure) in the Ellenburger Group, below the Barnett Shale. NEFZ, Newark east fault zone; SWD, saltwater disposal. Llano uplift, stipple pattern–Precambrian metasedimentary rocks; light gray, Ordovician carbonates. Seismicity shows clusters around Azle (Parker County), Irving-Dallas (Dallas County), and Venus (Johnson County). Faults from Ewing et al. (36).

  • Fig. 3 Generalized subsurface stratigraphic section of the central and eastern FWB.

    Most of the saltwater disposal in the FWB takes place in the Early Ordovician Ellenburger Group, close to the Precambrian basement where the majority of seismicity occurs. Few wells penetrate below the Ellenburger, and details of the Cambrian stratigraphy are from the Llano uplift, central Texas. The schematic stratigraphic column to the right shows the main horizons identified in the seismic reflection profiles shown in Figs. 4 and 5. Modified with permissions from Pollastro et al. (24) and Ewing (97).

  • Fig. 4 Seismic reflection data in the Venus, Texas, study area.

    (A) Location map of seismic reflection profiles near Venus, Texas, Johnson County (for location, see Fig. 2), showing interpreted faults at the top of the crystalline basement, the 2008–2016 relocated seismicity (colored circles) (32), the ANSS moment tensor location of the 2015 Mw 4.0 event (location uncertainty ± 4.5 km). SHmax orientation from Lund Snee and Zoback (42). Squares are saltwater disposal wells with production well numbers [American Petroleum Institute (API)]. (B) Unmarked time-migrated, depth-converted seismic reflection profiles. (C) Interpreted seismic reflection profiles. Red rectangles on wells show saltwater disposal injection depth intervals. Hypocentral locations (green circles) were projected only along line A. See Fig. 3 for corresponding stratigraphy in the FWB.

  • Fig. 5 Seismic reflection data in the Dallas-Irving, Texas, study area.

    (A) SMU earthquake catalog hypocentral locations projected onto the trace of the seismic profile near Irving, Texas (see map in Fig. 2). Depths of geological unit tops are based on nearby well logs. (B) Unmarked and interpreted time-migrated seismic reflection profile near Irving, Texas. Tops of stratigraphic units are constrained by the well ~500 m NE of the profile [star in (C)]. Black arrows show the two-way travel time (TWTT) of the horizontal time slice shown in (C). (C) Horizontal time slice at 2.076 s (TWTT) (normal polarity amplitude map at the top of crystalline basement) shows structures (marked by blue arrows) striking ~N40°E parallel to the general trend of the hypocenters in the basement (shown by circles, color-coded by depth) and to the average focal mechanism of the Dallas-Irving seismic sequence (N39°E). NW-SE black line shows the location of seismic profile in (B). Yellow star is the location of production well pad.

  • Fig. 6 The northern Mississippi embayment.

    The map shows the main tectonic features of the basin, the seismicity of the NMSZ [from the Center for Earthquake Research and Information (CERI) Catalog]. ERRM, eastern Reelfoot rift margin; MSF, Meeman-Shelby fault; NMNF, New Madrid North fault; WRRM, western Reelfoot rift margin. Location of Cambrian basement faults is from Thomas (48). Dashed rectangle shows location of Fig. 7.

  • Fig. 7 Seismic reflection data across the NMSZ.

    (A) Location map of the marine seismic reflection line M6 acquired along the Mississippi River, MO-155 well (orange star), and NMSZ seismicity (green circles). CGF, Cottonwood Grove fault. (B) Unmarked (top) and interpreted (bottom) seismic line M6. The Axial fault and the CGF deform the base of the Quaternary alluvium [marked by the Eocene/Quaternary unconformity (Q/Eo)], Cenozoic, and Mesozoic semi-consolidated sediments to the top of the Ordovician rocks. Vertical displacements increase with age of geologic unit on each fault from ~25 m at the base of the Quaternary to ~40 m at the top of the Cretaceous sediments to ~60 m at the top of the Ordovician rocks, indicating a long-lived history of deformation along both faults throughout the Cenozoic and possibly the Mesozoic (WG, Paleocene-Eocene Wilcox Group; Kr, Upper Cretaceous sediments; Pz, Ordovician sedimentary rocks). (C) Hypocenter locations (green circles) within 10 km of the seismic line projected onto the profile show the Axial fault as a vertical fault that extends to depths of 12 km beneath the seismic line. Focal mechanisms show predominant left-lateral strike-slip movement along the Axial fault. Whether the Axial fault and the Cottonwood Grove faults are two distinct structures at depth or part of a flower strike-slip system is still debated.

  • Table 1 Recurrence interval calculation for currently active FWB seismic sources.

    Fault dimensions were derived from the SMU earthquake catalog and detailed studies (19, 32). Seismic moment for each sequence was calculated using NEIC catalog local magnitudes (Mb_lg) (see table S1). Note that fault areas allow for larger maximum magnitudes than those recorded by the current seismic sequences (98). Larger magnitudes would translate into larger slip/sequence and therefore into longer return intervals for each seismic sequence. Therefore, by assuming that current seismic sequences are representative of past slip occurrences, our estimates for return times can be considered minimum values.

    SequenceStrike of
    Dip of
    extent (km)
    extent (km)
    area (km2)
    Moment of
    (dynes × cm)
    displacement in
    sequence (cm)
    number of
    interval (years)
    Azle225703.54.314.92.11 × 10220.39380478,866
    Irving39683.54.315.11.49 × 10220.28545455,003
    Venus220565.52.413.31.18 × 10220.25606849,440

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • table S1. USGS NEIC earthquake catalog.
    • table S2. Seismic reflection data parameters for lines A, B, and C in Johnson County, Texas, and Irving, Texas.

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