Article

Evaluating Spatial and Temporal Relations between an Earthquake Cluster near Entiat, Central Washington, and the Large December 1872 Entiat Earthquake

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We investigate spatial and temporal relations between an ongoing and prolific seismicity cluster in central Washington, near Entiat, and the 14 December 1872 Entiat earthquake, the largest historic crustal earthquake in Washington. A fault scarp produced by the 1872 earthquake lies within the Entiat cluster; the locations and areas of both the cluster and the estimated 1872 rupture surface are comparable. Seismic intensities and the 1–2 m of coseismic displacement suggest a magnitude range between 6.5 and 7.0 for the 1872 earthquake. Aftershock forecast models for (1) the first several hours following the 1872 earthquake, (2) the largest felt earthquakes from 1900 to 1974, and (3) the seismicity within the Entiat cluster from 1976 through 2016 are also consistent with this magnitude range. Based on this aftershock modeling, most of the current seismicity in the Entiat cluster could represent aftershocks of the 1872 earthquake. Other earthquakes, especially those with long recurrence intervals , have long-lived aftershock sequences, including the M w 7.5 1891 Nobi earthquake in Japan, with aftershocks continuing 100 yrs after the mainshock. Although we do not rule out ongoing tectonic deformation in this region, a long-lived aftershock sequence can account for these observations. Electronic Supplement: Interpretation of aeromagnetic data in the vicinity of the Entiat seismicity cluster and the 1872 earthquake.
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... The felt area of the 1936 earthquake is about half that estimated for the 18 October 1935 (local time) Helena earthquake , which has an ISC-GEM (2018; see Data and Resources) magnitude of M 6.2. An empirical intensity magnitude relation for Oregon and Washington in Brocher, Blakely, et al. (2017) suggests that a maximum MMI VII corresponds to an M 5.9 earthquake. This estimate is higher than the M 5.1-5.5 range determined from the intensity data by Bakun et al. (2002). ...
... 18 July 1936 (local time): it was assigned an MMI V at Helix, Oregon and was also felt at Athena, Milton-Freewater, Pendleton, and Stateline, Oregon, and at Dayton, Touchet, and Walla Walla, Washington (Table 5). Intensity-magnitude relationships in Oregon and Washington suggest its maximum MMI V is consistent with a duration magnitude (M D ) of 4.0 (Brocher, Blakely, et al., 2017). An MMI V was also assigned to the aftershock on 4 August 1936 : It was felt at Colfax, Waitsburg, and Walla Walla, Washington, and Helix, Milton-Freewater, and Pendleton, Oregon (Table 5). ...
... In the calculations shown in Figure 7a, we assume that the felt (MMI ≥ II) aftershocks have a minimum magnitude between M 2.7 and M D 2.5 (Bakun et al., 2002;Brocher, Blakely, et al., 2017). Although the expected numbers of M 2.5 and 2.7 aftershocks as a function of mainshock magnitude differ, they show similar rates of increase with magnitude (Fig. 7a). ...
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The epicenter of the 16 July 1936 M 6 Milton-Freewater earthquake, also known as the State Line earthquake and the largest historical earthquake in northeastern Oregon or southeastern Washington, is uncertain. Various studies place the epicenter of the earthquake, which was widely felt in eastern Washington, northeastern Oregon, and northern Idaho, within 30 km of the intersection of the Hite and Wallula faults. In the absence of reported coseismic surface rupture for the earthquake, we sought to determine which epicentral location is most consistent with the intensity observations and with its aftershock sequence, which lasted for at least 27 months. An epicenter between Umapine and Milton-Freewater best matches the observations. This location falls within the region that experienced the highest intensities of VII and reported the largest number of aftershocks, compares favorably to the (2018) International Seismological Centre-Global Earthquake Model (ISC-GEM) epicenter, and is proximal to sites that experienced ground failure and groundwater effects. Modeling of aftershock rates is consistent with this suggested epicenter and with the estimated 10 km long subsurface rupture of the earthquake. This suggested epicenter lies at, or just west of, the intersection of the Hite and Wallula faults. The elongation of ground failure along the Wallula fault and the aftershock distribution appears more consistent with rupture of the Wallula fault or of a subparallel fault than with rupture of the Hite fault. Rupture on faults to the north or east of the Wallula-Hite fault intersection is inconsistent with most observations, including the perceived impulsivity of the mainshock.
... This scarp, the Spencer Canyon scarp, located several kilometers southwest (SW) of Entiat, may resolve the location of the 1872 fault rupture and may indicate that its depth was sufficiently shallow to rupture to the surface. Brocher et al. (2017) investigated the spatial and temporal relationships between the 1872 earthquake and the ongoing Entiat seismicity cluster. They showed that the two share a common footprint and that aftershock forecast models for an 1872 M 6.5-7 earthquake are compatible with the ongoing seismicity in the cluster. ...
... This decrease is too small to match the estimated S-P times, which are several seconds early. Furthermore, as noted by Spence (1989), a crustal mainshock is suggested by the vigorous aftershock sequence (Brocher et al., 2017), making a lower crustal/upper mantle earthquake unlikely. ...
... L. Sherrod et al., unpublished manuscript, 2017; see Data and Resources). The center of a prolific ongoing seismicity cluster, consisting of shallow earthquakes between 3 and 8 km depth, lies just NE of Entiat (Brocher et al., 2017). Aftershock forecast models indicate that the earthquakes in this cluster could represent ongoing aftershocks of an 1872 earthquake near Entiat with M 6.5 (Brocher et al., 2017). ...
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Reported aftershock durations, earthquake effects, and other observations from the large December 14, 1872 earthquake in central Washington are consistent with an epicenter near Entiat, Washington. Only near Entiat were aftershocks reported lasting for more than 3 months. Modal intensity data described in this paper are consistent with an Entiat area epicenter, where the largest Modified Mercalli intensities, VIII, were assigned between Lake Chelan and Wenatchee. Although ground failures and water effects were widespread, there is a concentration of these features along the Columbia River and its tributaries in the Entiat area. Assuming linear raypaths, misfits from 23 reports of the directions of horizontal shaking have a local minima at Entiat, assuming the reports are describing surface waves, but the region having comparable misfit is large. Broadband seismograms recorded for comparable raypaths provide insight into the reasons why possible S-P times estimated from felt reports at two locations are several seconds too small to be consistent with an Entiat area epicenter.
... GPS vectors in the area around Entiat suggest that the Spencer Canyon fault is oriented somewhat oblique to the strain field, suggesting that earthquakes on the fault may have a lateral motion component that we were unable to resolve in the field. The 1872 CE Chelan earthquake and the 1936 CE Milton-Freewater earthquake in northeastern Oregon make the Yakima folds home to two M6 earthquakes in the past ∼150 years (Brocher & Sherrod, 2018;Brocher et al., 2017). A growing paleoseismologic catalog for the Yakima folds suggests that other active faults exist in the region (Blakely et al., 2011(Blakely et al., , 2014Kelsey et al., 2017;Sherrod et al., 2013Sherrod et al., , 2016Staisch et al., 2018). ...
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One of the largest historical earthquakes in the U.S. Pacific Northwest occurred on December 15, 1872 near the south end of Lake Chelan. Lack of recognized surface deformation suggested that the earthquake occurred on a blind, perhaps deep, fault. New LiDAR data revealed a NW‐side‐up scarp along the north side of Spencer Canyon near Entiat, Washington. Landslides triggered during the earthquake impounded small ponds in Spencer Canyon; the larger of the two landslides obliterated a portion of the scarp. Tree‐ring counts show that the oldest trees on each landslide are 130 and 128 years old, and lend credence to the idea that the earthquake triggered the landslides. Trenches across the scarp exposed a NW‐dipping thrust fault offsetting young soils and Mesozoic bedrock. Radiocarbon and tree ring data shows that the last fault movement was between 1856 and 1873 CE, and was most likely during the 1872 CE earthquake.
... Earthquake clusters have been identified in nearly all seismogenic areas worldwide (Basab, Sabyasachi, and Sujit, 2004;Sammis and Smith, 2013;Spicak and Vanek, 2013;Gan, Frohlich, and Jin, 2015;Brocher, Blakely, and Sherrod, 2017;Lisi et al., 2019;Mesimeri, Karakostas, Papadimitriou, and Tsaklidis, 2019). Most of these earthquake clusters are considered to have a tectonic origin, but some may be induced by oil and gas extraction (Phillips, Fairbanks, Rutledge, and Anderson, 1998;Lei et al., 2013;Foulger, Wilson, Gluyas, Julian, and Davies, 2018;Roach, 2018). ...
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... Geodetic data show that tectonic blocks along the northwestern margin of the United States rotate clockwise, due to Pacific-North America relative plate motion and oblique subduction of the Juan de Fuca plate beneath North America (Wells et al., 1998;Wells and Simpson, 2001;Mazzotti et al., 2002;McCaffrey et al., 2013McCaffrey et al., , 2016Brocher et al., 2017;Fig. 1). ...
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... Indeed, earthquakes independent of their size can trigger other earthquakes, with no distinction in the physical relaxation mechanism between triggered events and other earthquakes (Hough and Jones, 1997). These triggered earthquakes may occur after a time delay that can range from seconds to years after the causative event (Freed, 2005;Brocher et al., 2017). The detailed physics of interearthquake triggering is complex, but the general idea is that earthquakes perturb the state of stress of neighboring faults and modify the mechanical condition of active faults (Freed, 2005). ...
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The extent to which ongoing seismicity in intraplate regions represents long-lived aftershock activity is unclear. We examined historical and instrumental seismicity in the New Madrid central U.S. region to determine whether present-day seismicity is composed predominantly of aftershocks of the 1811–1812 earthquake sequence. High aftershock productivity is required both to match the observation of multiple mainshocks and to explain the modern level of activity as aftershocks; synthetic sequences consistent with these observations substantially overpredict the number of events of magnitude ≥ 6 that were observed in the past 200 years. Our results imply that ongoing background seismicity in the New Madrid region is driven by ongoing strain accrual processes and that, despite low deformation rates, seismic activity in the zone is not decaying with time.
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Generic Mapping Tools (GMT) is an open-source software package for the analysis and display of geoscience data, helping scientists to analyze, interpolate, filter, manipulate, project, and plot time series and gridded data sets. The GMT toolbox includes about 80 core and 40 supplemental program modules sharing a common set of command options, file structures, and documentation. Its power to process data and produce publication-quality graphic presentations has made it vital to a large scientific community that now includes more than 25,000 individual users. GMT's website (http://gmt.soest.hawaii.edu/) exceeds 20,000 visits per month, and server logs show roughly 2000 monthly downloads.
Article
Intensity data from 14 historic earthquakes in or near Washington State, as reported at over 300 localities, are used to study the attenuation structure in Washington. The empirical relation of Evernden (Bull. Seism. Soc. Am., 65, 1287-1313(1975)) is used to determine the size and depth for each earthquake and the local attenuation factor, k, for two physiographic parts of the state. The value for k in the Puget Sound region and north into Canada is 1 3/4, while k = 1 1/2 is more appropriate for eastern Washington and northern Oregon. Individual amplification factors are computed for all localities at which four or more earthquakes have been felt by averaging the difference between the computed intensity and reported intensity at each site. Using these correction factors, the intensities for the North Cascade earthquake of 1872 are used to place constraints on its size and location. It appears this earthquake may be slightly larger (magnitude 7.4) and located south and west of the original epicenter determined by Milne. 7 figures, 4 tables.
Article
A straightforward method for computing rates of slip from earthquakes in major fault zones is presented. The slip rate is calculated from the sum of moments for the earthquakes. Rates obtained are in approximate agreement with rates obtained from geodetic measurements or magnetic anomalies, provided that long time samples are considered and provided that adjustments are made in the vertical extent of the zone of earthquake generation. For some fault zones, particularly deep island arc shear zones, strain is perhaps being relieved by steady creep, whereas, in other fault zones, e.g., the San Andreas, strain is accumulating for a large earthquake. The zone of earthquake generation for oceanic transform faults may be as little as 5 km in vertical extent.
Article
Using a magnitude (M)-log area (A) dataset augmented with seven large (M > 7.0) earthquakes occurring since Wells and Coppersmith (1994), this short note assesses the current validity of the bilinear M-log A relations for continental, strike-slip earthquakes proposed by Hanks and Bakun (2002), in particular the L-model scaling at M > 7. The relations determined by Hanks and Bakun (2002) are only insignificantly altered, leaving these bilinear M-log A relations as valid now as when first proposed.
Article
The Wells and Coppersmith (1994) M -log A data set for continental earthquakes (where M is moment magnitude and A is fault area) and the regression lines derived from it are widely used in seismic hazard analysis for estimating M , given A . Their relations are well determined, whether for the full data set of all mechanism types or for the subset of strike-slip earthquakes. Because the coefficient of the log A term is essentially 1 in both their relations, they are equivalent to constant stress-drop scaling, at least for M ≤ 7, where most of the data lie. For M > 7, however, both relations increasingly underestimate the observations with increasing M . This feature, at least for strike-slip earthquakes, is strongly suggestive of L-model scaling at large M . Using constant stress-drop scaling (Δσ = 26.7 bars) for M ≤ 6.63 and L-model scaling (average fault slip ū = α L , where L is fault length and α = 2.19 &times 10-5) at larger M , we obtain the relations \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $\mathbf{M}=\mathrm{log}{\ }A+3.98{\pm}0.03,{\ }A{\leq}537{\ }\mathrm{km}^{2}$ \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $\mathbf{M}=4{/}3{\ }\mathrm{log}{\ }A+3.07{\pm}0.04,{\ }A{>}537{\ }\mathrm{km}^{2}.$ \end{document} These prediction equations of our bilinear model fit the Wells and Coppersmith (1994) data set well in their respective ranges of validity, the transition magnitude corresponding to A = 537 km2 being M = 6.71. Manuscript received 15 April 2001.
Article
Seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stressing history control the timing of earthquakes. The model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate- and state-dependent fault properties. This yields a general state-variable constitutive formulation for rate of earthquake production resulting from an applied stressing history. To illustrate and test the model some characteristics of seismicity following a stress step have been explored. It is proposed that various features of earthquake clustering arise from sensitivity of nucleation times to the stress changes induced by prior earthquakes. The model gives the characteristic Omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate. Earthquake data appear to support a model prediction that aftershock duration, defined as the time for rates to return to the back-ground seismicity rate, is proportional to mainshock recurrence time. Observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial dependence of stress changes of the first event of the pair and stress-sensitive time-dependent nucleation. Applications of the constitutive formulation are not restricted to the simple stress step models investigated here. It may be applied to stressing histories of arbitrary complexity. The apparent success at modeling clustering phenomena suggests the possibility of using the formulation to estimate short- to intermediate-term earthquake probabilities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress.
Article
Article
The historical and instrumental records of earthquakes were used to estimate earthquake recurrence rates for input to a new seismic hazard analysis at the Hanford Site in eastern Washington. Two areas were evaluated, the eastern Washington region and the smaller Yakima Fold Belt, in which the Hanford Site is located. The completeness of a catalog of earthquakes was evaluated for earthquakes with Modified Mercalli Intensity (MMI) IV through VII. Only one MMI VII earthquake was reported in the last 100 years in eastern Washington. The reporting of MMI VI earthquakes appears to be complete for the last 80 years, and the reporting of MMI V earthquakes appears to be complete for the last 65 years. However, MMI IV earthquakes are consistently under-reported. For a limited set of earthquakes, both MMI and magnitude (M/sub L/) have been reported. A plot of these data indicated that the Gutenberg-Richter relationship could be used to estimate earthquakes magnitudes from intensities. A recurrence curve for the historical earthquake data was calculated using the maximum likelihood method, including corrections for the width of the magnitude conversion. The slope of the recurrence curve (i.e., b-value) was found to be -1.15. Another catalog, one that listed instrumentally detected earthquakes from 1969 to the present, was used to supplement the historical earthquake data. Magnitudes were determined using a coda-length method (M/sub c/) that had been approximately calibrated to local magnitude M/sub L/. For earthquakes whose M/sub c/ was between 3 and 5, the b-value ranged from -1.07 to - 1.12. 12 refs., 9 figs., 9 tabs.
Article
The large dispersion of data for components of earthquake motion requires that the spread be appraised in design applications. Instrumental data also must be related to historic records of intensity. The near field and the far field contribute greatly to differences in peak motions. Site conditions, soil versus rock, affect duration. With these considerations, and with geological studies and the probability of recurrence, peak values can be specified from parameters of motions related to Modified Mercalli intensities. These peak values can be used for rescaling selected strong motion records or alternatively for the generation of synthetic seismograms. The procedure incorporates the wide variability in ground motions that have occurred during earthquakes. (Author)
Article
After a strong earthquake, the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures. A stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock. The probabilities depend strongly on the model parameters, which are estimated with Bayesian statistics from both the ongoing aftershock sequence and from a suite of historic California aftershock sequences. Probabilities for damaging aftershocks and greater mainshocks are typically well-constrained after the first day of the sequence, with accuracy increasing with time.
The December 14, 1872, earthquake in the Pacific Northwest
• S T Hopper
• D M Algermissen
• S R Perkins
• E P Brockman
• Arnold
The other data are available in the unpublished USGS openfile report by M. G. Hopper, S. T. Algermissen, D. M. Perkins, S. R. Brockman, and E. P. Arnold (2003), "The December 14, 1872, earthquake in the Pacific Northwest", and in the unpublished manuscript by B. L. Sherrod, R. J. Blakely, and C. S.
Active faulting in the northern Juan de Fuca Strait, implications for Victoria
• V Barrie
• G Greene
Barrie, V., and G. Greene (2015). Active faulting in the northern Juan de Fuca Strait, implications for Victoria, British Columbia, Geol. Surv. Can. Curr. Res. 2015-6, 10, doi: 10.4095/296564.
Scaling for seismic source spectra and energy attenuation in the Chelan Region, eastern Washington
• S S Bor
Bor, S. S. (1977). Scaling for seismic source spectra and energy attenuation in the Chelan Region, eastern Washington, Master Dissertation, University of Washington, Seattle, 65 pp.
Active fault monitoring using portable seismograph arrays in Washington State
• R Cakir
• S Scott
• T J Walsh
• T Lau
• K Szatkowski
• J Dragovich
• M L Anderson
• M Polenz
• S Mavor
• M Allen
Cakir, R., S. Scott, T. J. Walsh, T. Lau, K. Szatkowski, J. Dragovich, M. L. Anderson, M. Polenz, S. Mavor, and M. Allen (2016). Active fault monitoring using portable seismograph arrays in Washington State, Eos Trans. AGU 98, Abstract T41A-2892.
Reportof the Review Panel on the December 14, 1872 earthquake in Washington Public Power Supply System Nuclear Projects Nos. 1 and 4, Preliminary Site Analysis Report
• H A Coombs
• W G Milne
• O W Nuttli
• D B Slemmons
Coombs,H.A., W. G.Milne,O.W. Nuttli, and D.B.Slemmons(1976). Reportof the Review Panel on the December 14, 1872 earthquake in Washington Public Power Supply System Nuclear Projects Nos. 1 and 4, Preliminary Site Analysis Report, Amendment 23, Vol. 2A, Sub-appendix 2R-A, 30 pp., Appendix B, Reports related to the December 14, 1872 earthquake, 247 pp., Report to the Nuclear RegulatoryCommission, Washington, D.C.
The Chelan seismic zone, the Great Terrace and the December 1872 Washington State
• J G Crider
• R S Crosson
• J Brooks
Crider, J. G., R. S. Crosson, and J. Brooks (2003). The Chelan seismic zone, the Great Terrace and the December 1872 Washington State, Geol. Soc. Am. Abstr. Progr. 35, no. 6, 645.
An InSAR analysis of surface deformation associated with the Chelan seismic zone, central Washington
• A Diefenbach
• J G Crider
• M Poland
Diefenbach, A., J. G. Crider, and M. Poland (2007). An InSAR analysis of surface deformation associated with the Chelan seismic zone, central Washington, Proc. of the GSA Cordilleran Section 103rd Annual Meeting, Geol. Soc. Am., Bellingham, Washington, 4-6 May.
Seismic Activity in Canada West of the 113th Meridian
• W G Milne
Milne, W. G. (1956). Seismic Activity in Canada West of the 113th Meridian, 1841-1951, Vol. 18, Dominion Observatory Publications, Ottawa, Canada, 126-127.
LiDAR helps identify source of 1872 earthquake near Chelan
• B L Sherrod
• R J Blakely
• C S Weaver
Sherrod, B. L., R. J. Blakely, and C. S. Weaver (2015). LiDAR helps identify source of 1872 earthquake near Chelan, Eos Trans. AGU 97, Abstract T31A-2826.