{"key":"quakes","title":"The ground, shaking","headline":{"value":"every 4 years","label":"a magnitude-5 earthquake within 150 km of Chico — 13 since 1970 in the USGS catalogue, and the Gutenberg–Richter law fitted to the 4,294 events outside the Geysers' induced swarm (b = 1.12) puts a magnitude 6 at about one every 92 years; the last was 2026's M5.6 near Redwood Valley; the closest big one, the 1975 Oroville M5.7, 41 km away, is the textbook case of a reservoir setting off a fault"},"facts":{"n":7864,"since":"1970-01-01","radiusKm":150,"minMag":2.5,"years":56.8,"mc":2.8,"mcAll":2.8,"nTectonic":4294,"bValue":1.123,"bErr":0.024,"aValue":4.772,"bValueAbove4":0.934,"bErrAbove4":0.073,"nAbove4":121,"bValueAll":1.168,"bErrAll":0.018,"aValueAll":5.145,"rateM4":1.908,"rateM5":0.144,"rateM6":0.011,"countM4":173,"countM5":13,"countM6":0,"returnM5Years":7,"returnM6Years":92,"countedReturnM5Years":4.4,"largestMag":5.7,"largestPlace":"The 1975 Oroville, California Earthquake","largestDate":"1975-08-01","largestKm":41,"nearestM4Mag":4,"nearestM4Place":"11 km E of Artois, California","nearestM4Date":"1997-10-25","nearestM4Km":24,"orovilleKm":41.4,"orovilleMag":5.7,"orovilleDate":"1975-08-01","within25km":115,"nearGeysers":3570,"medianDepthKm":3,"lastM5Mag":5.59,"lastM5Place":"11 km N of Redwood Valley, CA","lastM5Date":"2026-06-24"},"series":{"gr":[{"mag":2.8,"cumN":2414,"fitN":2414},{"mag":2.9,"cumN":1921,"fitN":1864},{"mag":3,"cumN":1466,"fitN":1439.3},{"mag":3.1,"cumN":1076,"fitN":1111.4},{"mag":3.2,"cumN":822,"fitN":858.2},{"mag":3.3,"cumN":633,"fitN":662.6},{"mag":3.4,"cumN":486,"fitN":511.7},{"mag":3.5,"cumN":379,"fitN":395.1},{"mag":3.6,"cumN":296,"fitN":305.1},{"mag":3.7,"cumN":219,"fitN":235.6},{"mag":3.8,"cumN":180,"fitN":181.9},{"mag":3.9,"cumN":143,"fitN":140.4},{"mag":4,"cumN":121,"fitN":108.4},{"mag":4.1,"cumN":99,"fitN":83.7},{"mag":4.2,"cumN":84,"fitN":64.7},{"mag":4.3,"cumN":71,"fitN":49.9},{"mag":4.4,"cumN":57,"fitN":38.6},{"mag":4.5,"cumN":43,"fitN":29.8},{"mag":4.6,"cumN":35,"fitN":23},{"mag":4.7,"cumN":29,"fitN":17.7},{"mag":4.8,"cumN":19,"fitN":13.7},{"mag":4.9,"cumN":16,"fitN":10.6},{"mag":5,"cumN":13,"fitN":8.2},{"mag":5.1,"cumN":12,"fitN":6.3},{"mag":5.2,"cumN":8,"fitN":4.9},{"mag":5.3,"cumN":5,"fitN":3.8},{"mag":5.4,"cumN":4,"fitN":2.9},{"mag":5.5,"cumN":4,"fitN":2.2},{"mag":5.6,"cumN":3,"fitN":1.7},{"mag":5.7,"cumN":2,"fitN":1.3}],"yearly":[{"year":1970,"n":0},{"year":1971,"n":0},{"year":1972,"n":0},{"year":1973,"n":4},{"year":1974,"n":34},{"year":1975,"n":565},{"year":1976,"n":105},{"year":1977,"n":155},{"year":1978,"n":155},{"year":1979,"n":55},{"year":1980,"n":121},{"year":1981,"n":130},{"year":1982,"n":158},{"year":1983,"n":175},{"year":1984,"n":150},{"year":1985,"n":188},{"year":1986,"n":163},{"year":1987,"n":159},{"year":1988,"n":138},{"year":1989,"n":161},{"year":1990,"n":137},{"year":1991,"n":143},{"year":1992,"n":176},{"year":1993,"n":132},{"year":1994,"n":147},{"year":1995,"n":160},{"year":1996,"n":131},{"year":1997,"n":148},{"year":1998,"n":212},{"year":1999,"n":192},{"year":2000,"n":224},{"year":2001,"n":149},{"year":2002,"n":127},{"year":2003,"n":147},{"year":2004,"n":138},{"year":2005,"n":138},{"year":2006,"n":160},{"year":2007,"n":168},{"year":2008,"n":147},{"year":2009,"n":117},{"year":2010,"n":133},{"year":2011,"n":121},{"year":2012,"n":129},{"year":2013,"n":258},{"year":2014,"n":98},{"year":2015,"n":116},{"year":2016,"n":126},{"year":2017,"n":104},{"year":2018,"n":87},{"year":2019,"n":117},{"year":2020,"n":108},{"year":2021,"n":140},{"year":2022,"n":103},{"year":2023,"n":164},{"year":2024,"n":126},{"year":2025,"n":94},{"year":2026,"n":131}],"big":[{"date":"1973-11-12","mag":4.8,"place":"7 km S of Willits, California","km":138,"lat":39.343,"lon":-123.363},{"date":"1974-05-27","mag":4.6,"place":"9 km S of East Quincy, California","km":80,"lat":39.852,"lon":-120.91},{"date":"1974-09-29","mag":4.7,"place":"2 km N of Spring Garden, California","km":92,"lat":39.914,"lon":-120.788},{"date":"1975-08-01","mag":4.7,"place":"2 km NNW of Palermo, California","km":39,"lat":39.453,"lon":-121.548},{"date":"1975-08-01","mag":4.5,"place":"0 km WSW of Palermo, California","km":41,"lat":39.432,"lon":-121.546},{"date":"1975-08-01","mag":5.7,"place":"The 1975 Oroville, California Earthquake","km":41,"lat":39.432,"lon":-121.546},{"date":"1975-08-01","mag":4.7,"place":"0 km ENE of Palermo, California","km":42,"lat":39.439,"lon":-121.528},{"date":"1975-08-01","mag":4.6,"place":"0 km ENE of Palermo, California","km":42,"lat":39.439,"lon":-121.528},{"date":"1975-08-02","mag":5.1,"place":"5 km ENE of Palermo, California","km":44,"lat":39.449,"lon":-121.479},{"date":"1975-08-02","mag":5.2,"place":"4 km E of Palermo, California","km":44,"lat":39.438,"lon":-121.485},{"date":"1975-08-03","mag":4.6,"place":"3 km ESE of South Oroville, California","km":38,"lat":39.486,"lon":-121.519},{"date":"1975-08-06","mag":4.7,"place":"1 km E of South Oroville, California","km":36,"lat":39.496,"lon":-121.539},{"date":"1975-08-08","mag":4.9,"place":"3 km WSW of Oroville East, California","km":38,"lat":39.501,"lon":-121.512},{"date":"1975-09-27","mag":4.6,"place":"1 km ENE of Oroville, California","km":35,"lat":39.52,"lon":-121.538},{"date":"1976-06-24","mag":4.7,"place":"3 km NNE of Johnstonville, California","km":132,"lat":40.418,"lon":-120.578},{"date":"1977-11-22","mag":4.8,"place":"8 km E of Willits, California","km":127,"lat":39.409,"lon":-123.257},{"date":"1978-03-26","mag":4.5,"place":"4 km SE of Calpella, California","km":127,"lat":39.209,"lon":-123.156},{"date":"1979-02-22","mag":5.3,"place":"4 km S of Doyle, California","km":150,"lat":39.986,"lon":-120.113},{"date":"1980-11-28","mag":5.1,"place":"8 km SSW of Kingvale, California","km":130,"lat":39.252,"lon":-120.454},{"date":"1985-12-28","mag":4.62,"place":"10 km SSE of Sierra City, California","km":112,"lat":39.484,"lon":-120.567},{"date":"1986-08-01","mag":4.67,"place":"5 km NNE of Brooktrails, California","km":133,"lat":39.489,"lon":-123.361},{"date":"1995-09-04","mag":4.8,"place":"13 km SW of Middletown, California","km":140,"lat":38.683,"lon":-122.743},{"date":"1998-07-21","mag":4.5,"place":"4 km NNW of Redding, California","km":111,"lat":40.626,"lon":-122.409},{"date":"1998-11-26","mag":5.1,"place":"7km NW of Redding, CA","km":111,"lat":40.626,"lon":-122.414},{"date":"1998-11-26","mag":4.62,"place":"5km NNW of Redding, CA","km":110,"lat":40.617,"lon":-122.398},{"date":"2000-01-11","mag":4.59,"place":"6 km N of Geyserville, California","km":141,"lat":38.769,"lon":-122.914},{"date":"2001-08-10","mag":5.2,"place":"3 km N of Blairsden, California","km":105,"lat":39.811,"lon":-120.617},{"date":"2004-02-18","mag":4.58,"place":"4 km WNW of Cobb, California","km":127,"lat":38.837,"lon":-122.767},{"date":"2006-05-12","mag":4.71,"place":"7 km W of Cobb, California","km":132,"lat":38.817,"lon":-122.814},{"date":"2006-10-20","mag":4.56,"place":"7 km NW of Cobb, California","km":126,"lat":38.867,"lon":-122.787},{"date":"2007-04-18","mag":4.79,"place":"15 km N of Potter Valley, California","km":113,"lat":39.465,"lon":-123.107},{"date":"2008-01-19","mag":4.5,"place":"34 km WNW of Rancho Tehama Reserve, California","km":92,"lat":40.167,"lon":-122.759},{"date":"2008-01-19","mag":4.7,"place":"31 km NW of Rancho Tehama Reserve, California","km":89,"lat":40.178,"lon":-122.704},{"date":"2008-12-26","mag":4.5,"place":"3 km NE of East Quincy, California","km":87,"lat":39.96,"lon":-120.869},{"date":"2011-10-27","mag":4.73,"place":"3 km WSW of Sattley, California","km":118,"lat":39.606,"lon":-120.471},{"date":"2012-09-25","mag":4.51,"place":"3 km N of Talmage, California","km":130,"lat":39.168,"lon":-123.166},{"date":"2013-05-24","mag":5.69,"place":"2 km NNE of Canyondam, California","km":84,"lat":40.192,"lon":-121.059},{"date":"2013-05-24","mag":4.86,"place":"1km NNW of Canyondam, CA","km":82,"lat":40.18,"lon":-121.078},{"date":"2014-01-12","mag":4.53,"place":"8 km W of Cobb, California","km":132,"lat":38.814,"lon":-122.816},{"date":"2016-08-10","mag":5.09,"place":"20 km NNE of Upper Lake, California","km":94,"lat":39.329,"lon":-122.802},{"date":"2016-12-14","mag":5.01,"place":"10 km W of Cobb, California","km":133,"lat":38.822,"lon":-122.841},{"date":"2021-05-07","mag":4.65,"place":"19km NW of Truckee, CA","km":134,"lat":39.461,"lon":-120.314},{"date":"2023-05-11","mag":5.48,"place":"Lake Almanor Earthquake","km":82,"lat":40.204,"lon":-121.109},{"date":"2023-05-12","mag":5.16,"place":"4km NW of Canyondam, CA","km":82,"lat":40.196,"lon":-121.1},{"date":"2023-09-08","mag":4.99,"place":"12 km NE of Burney, CA","km":138,"lat":40.953,"lon":-121.56},{"date":"2025-01-02","mag":4.65,"place":"4 km NW of Cobb, CA","km":126,"lat":38.846,"lon":-122.756},{"date":"2025-12-29","mag":4.7,"place":"15 km NNW of Susanville, CA","km":133,"lat":40.547,"lon":-120.701},{"date":"2025-12-31","mag":4.92,"place":"15 km NNW of Susanville, CA","km":133,"lat":40.544,"lon":-120.692},{"date":"2026-06-24","mag":5.59,"place":"11 km N of Redwood Valley, CA","km":126,"lat":39.362,"lon":-123.229}]},"sources":[{"name":"USGS ANSS Comprehensive Earthquake Catalog (ComCat), FDSN event web service","url":"https://earthquake.usgs.gov/fdsnws/event/1/query?format=csv&latitude=39.7285&longitude=-121.8375&maxradiuskm=150&starttime=1970-01-01&minmagnitude=2.5&orderby=time","note":"earthquakes of M2.5+ within 150 km of 39.7285, -121.8375 since 1970-01-01"},{"name":"Aki, K. (1965) \"Maximum likelihood estimate of b in the formula log N = a − bM and its confidence limits\", Bulletin of the Earthquake Research Institute 43:237","url":"https://scholar.google.com/scholar?q=Aki+1965+%22Maximum+likelihood+estimate+of+b%22"},{"name":"Shi, Y. & Bolt, B.A. (1982) \"The standard error of the magnitude-frequency b value\", Bulletin of the Seismological Society of America 72:1677","url":"https://doi.org/10.1785/BSSA0720051677"},{"name":"Bufe, C.G., Lester, F.W., Lahr, K.M., Lahr, J.C., Seekins, L.C. & Hanks, T.C. (1976) \"Oroville earthquakes: normal faulting in the Sierra Nevada foothills\", Science 192:72","url":"https://doi.org/10.1126/science.192.4234.72"}],"method":"Every earthquake of magnitude 2.5 or more within 150 km of downtown Chico since 1970 in the USGS catalogue: 7,864 events over 56.8 years. Counted by size they follow the Gutenberg–Richter relation log10 N = a − b·M — each step down in magnitude brings roughly ten times as many quakes, and b says exactly how many. b is Aki's maximum-likelihood estimate over the events at or above the completeness magnitude Mc = 2.8 (the size below which the network misses some, taken as the fullest 0.1 bin plus 0.2), with Shi and Bolt's standard error, fitted to the 4,294 events outside a 20 km circle around the Geysers; the fitted return periods are that line read at M5 and M6, an extrapolation from small quakes that assumes the past 57 years are typical. The circle takes in the Geysers geothermal field in the west (3,570 of the events, set off by water injected into hot rock), the Lake Almanor quakes of 2013 and 2023 in the north-east, and Lake Oroville, whose 1975 M5.7 is widely attributed to the filling of the reservoir — reservoir-induced seismicity, as Bufe and colleagues argued in 1976. The headline is counted, not fitted: M5 or more has come 13 times in 56.8 years, one every 4.4 years; the fitted line, made without the Geysers, puts M5 at one every 7 years and M6 at one every 92 (with the Geysers left in, b would read 1.17 and the line would run faster).","fetched_at":"2026-11-02T06:21:34.235Z"}