💾 Archived View for federal.cx › earthquake.gmi captured on 2024-08-18 at 17:05:09. Gemini links have been rewritten to link to archived content
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Earthquake Magnitude Scale Magnitude Earthquake Effects Number/year(est.) 2.5 or less Usually not felt, but can be recorded by seismograph. 900,000 2.5 to 5.4 Often felt, but only causes minor damage. 30,000 5.5 to 6.0 Slight damage to buildings and other structures. 500 6.1 to 6.9 May cause a lot of damage in very populated areas. 100 7.0 to 7.9 Major earthquake. Serious damage. 20 8.0 or greater Great earthquake. Total destruction near epicenter. One every 5 to 10 years Earthquake Magnitude Classes Earthquakes are also classified in categories ranging from minor to great. Class Magnitude Great 8 or more Major 7 - 7.9 Strong 6 - 6.9 Moderate 5 - 5.9 Light 4 - 4.9 Minor 3 - 3.9
(GMT, m > 1.7, 60sec)
08/18 20:57:44 2.46ml 24 km SW of Lamont, CA (35.1125 -119.1012)
08/18 20:09:15 1.71ml 6 km SSW of Volcano, Hawaii (19.3848 -155.2530)
08/18 19:40:04 1.74ml 6 km SSW of Volcano, Hawaii (19.3842 -155.2537)
08/18 19:28:20 4.40mb 17 km S of San Mateo del Mar, Mexico (16.0523 -94.9727)
08/18 19:13:00 2.00ml 65 km NNE of Van Horn, Texas (31.5730 -104.5400)
08/18 18:54:24 1.78ml 6 km SSW of Volcano, Hawaii (19.3865 -155.2495)
08/18 18:44:00 4.50mb 156 km WNW of Tobelo, Indonesia (2.1882 126.6833)
08/18 18:33:40 4.40mb 71 km WNW of Merredin, Australia (-31.1853 117.6124)
08/18 18:05:38 4.60mb 62 km WNW of Merredin, Australia (-31.2599 117.6740)
08/18 17:50:09 2.16ml 22 km W of Kalaoa, Hawaii (19.7425 -156.1930)
08/18 17:40:33 1.90ml 34 km SW of Coyanosa, Texas (31.0450 -103.3390)
08/18 17:20:47 1.90ml 13 km NE of Pāhala, Hawaii (19.2748 -155.3700)
08/18 17:06:26 1.75ml 6 km SSW of Volcano, Hawaii (19.3842 -155.2537)
08/18 15:58:57 3.41md 46 km N of Charlotte Amalie, U.S. Virgin Islands (18.7645 -64.9665)
08/18 15:50:49 5.00mb 14 km ESE of Daigo, Japan (36.7123 140.4958)
08/18 15:48:21 4.70mb 13 km ENE of Daigo, Japan (36.7981 140.4916)
08/18 15:27:16 4.80mb 19 km ESE of Nabire, Indonesia (-3.4335 135.6596)
08/18 15:07:46 2.63ml 43 km SE of Pāhala, Hawaii (18.9180 -155.1983)
08/18 15:05:43 2.47ml 24 km NW of Grapevine, CA (35.0998 -119.1037)
08/18 14:50:17 2.30ml 52 km N of Petersville, Alaska (62.9649 -150.7755)
08/18 14:39:40 2.80ml 10 km SSW of Progreso, B.C., MX (32.4925 -115.6087)
08/18 14:35:27 2.81md 1 km WSW of Indios, Puerto Rico (17.9885 -66.8282)
08/18 13:55:13 2.69ml 15 km S of Fern Forest, Hawaii (19.3305 -155.1140)
08/18 13:44:40 2.09md 13 km ESE of Pāhala, Hawaii (19.1432 -155.3705)
08/18 13:03:48 1.88ml 12 km WSW of Ojai, CA (34.4010 -119.3660)
08/18 13:01:48 2.25md 21 km WNW of Rincón, Puerto Rico (18.3978 -67.4452)
08/18 12:54:11 1.80ml 63 km W of Anchor Point, Alaska (59.7730 -152.9544)
08/18 12:50:57 4.30mb south of the Fiji Islands (-24.3651 179.9351)
08/18 12:50:00 2.50ml 97 km WSW of Pelican, Alaska (57.7871 -137.8396)
08/18 12:04:44 1.97ml 24 km SW of Lamont, CA (35.1092 -119.1063)
08/18 11:33:59 1.77md 20 km W of Volcano, Hawaii (19.4592 -155.4280)
08/18 11:24:15 2.06ml 6 km SW of Volcano, Hawaii (19.4093 -155.2820)
08/18 11:03:47 2.46ml 23 km SW of Lamont, CA (35.1072 -119.0885)
08/18 11:02:51 1.74ml 6 km SW of Volcano, Hawaii (19.4075 -155.2882)
08/18 10:57:07 4.40mb 23 km E of Farkhār, Afghanistan (36.5372 70.1132)
08/18 10:28:58 4.40mb 89 km E of Petropavlovsk-Kamchatsky, Russia (52.9206 159.9422)
08/18 09:36:20 2.45md 3 km E of The Geysers, CA (38.7843 -122.7270)
08/18 09:15:22 4.50mb 4 km ESE of Salvacion, Philippines (8.6964 126.2435)
08/18 08:52:41 4.70mb South Georgia Island region (-55.1545 -31.2050)
08/18 08:38:34 1.76ml 1 km NNW of View Park-Windsor Hills, CA (34.0035 -118.3530)
08/18 08:38:24 1.80ml 32 km W of Venetie, Alaska (67.0489 -147.1597)
08/18 08:35:53 3.43md 75 km N of Charlotte Amalie, U.S. Virgin Islands (19.0222 -64.8935)
08/18 08:35:51 1.91md 10 km E of Pāhala, Hawaii (19.1863 -155.3802)
08/18 08:29:58 1.78ml 11 km SW of Searles Valley, CA (35.6923 -117.4840)
08/18 08:29:08 1.80ml 42 km ENE of Susitna North, Alaska (62.3551 -149.1542)
08/18 08:14:49 2.70ml 42 km ENE of Pedro Bay, Alaska (59.9522 -153.4152)
08/18 08:11:43 1.73ml 20 km NW of Grapevine, CA (35.0917 -119.0625)
08/18 08:07:58 2.58md 6 km SE of La Parguera, Puerto Rico (17.9423 -66.9987)
08/18 08:06:17 3.01md 5 km ESE of La Parguera, Puerto Rico (17.9598 -66.9983)
08/18 07:13:23 1.80ml 35 km NNW of Toyah, Texas (31.5990 -103.9590)
08/18 06:48:42 4.30mb 50 km W of Abra Pampa, Argentina (-22.7936 -66.1824)
08/18 06:00:38 3.73md 102 km NE of Miches, Dominican Republic (19.6153 -68.3386)
08/18 06:00:17 3.70ml 153 km ESE of Cordova, Alaska (60.0304 -143.1757)
08/18 05:40:37 2.26md 10 km SE of Pāhala, Hawaii (19.1467 -155.3988)
08/18 05:33:42 4.80mb southeast of Easter Island (-41.2459 -89.5239)
08/18 05:19:08 3.40ml 94 km SSW of False Pass, Alaska (54.0504 -163.8839)
08/18 04:58:16 4.80mb Bonin Islands, Japan region (27.5797 143.0915)
08/18 04:33:09 1.80md 10 km NNE of Cloverdale, CA (38.8932 -123.0065)
08/18 04:10:18 4.40mb 9 km ENE of Honoria, Peru (-8.7465 -74.6250)
08/18 03:21:05 4.30mb 44 km E of Petropavlovsk-Kamchatsky, Russia (53.0430 159.2897)
08/18 03:17:45 2.09ml 9 km SE of Volcano, Hawaii (19.3688 -155.1807)
08/18 03:08:53 1.78ml 9 km ESE of Bodfish, CA (35.5510 -118.4068)
08/18 02:56:59 1.79md 10 km S of Pāhala, Hawaii (19.1130 -155.4652)
08/18 02:47:54 4.30mb 39 km SSW of San Pedro, Peru (-15.0725 -74.2821)
08/18 02:26:17 2.70ml 38 km S of Porvenir, Mexico (30.8954 -105.8150)
08/18 01:59:25 1.74ml 6 km SSW of Volcano, Hawaii (19.3892 -155.2495)
08/18 01:59:19 1.74ml 6 km SSW of Volcano, Hawaii (19.3888 -155.2543)
08/18 01:44:38 4.80mb 51 km NNW of Camiña, Chile (-18.8861 -69.6099)
08/18 01:34:13 2.61ml 14 km NNE of Lyman, Washington (48.6555 -122.0138)
08/18 00:16:26 4.40mb 71 km E of Petropavlovsk-Kamchatsky, Russia (53.0579 159.6908)
08/17 23:50:09 2.81md 20 km NNE of Arecibo, Puerto Rico (18.6468 -66.6527)
08/17 23:15:12 1.94ml 8 km SE of Volcano, Hawaii (19.3777 -155.1837)
08/17 23:12:59 2.49md 5 km S of Guánica, Puerto Rico (17.9190 -66.9123)
08/17 22:51:58 4.40mb 29 km SE of Jurm, Afghanistan (36.6619 71.0467)
08/17 22:46:53 1.86ml 7 km S of Volcano, Hawaii (19.3765 -155.2257)
08/17 22:27:10 5.10mb 94 km E of Petropavlovsk-Kamchatsky, Russia (52.9425 160.0187)
08/17 22:10:31 1.99ml 5 km SW of Volcano, Hawaii (19.4007 -155.2642)
08/17 22:10:24 2.67ml 9 km ESE of Pāhala, Hawaii (19.1630 -155.3977)
08/17 22:10:03 2.29ml 9 km SSE of Volcano, Hawaii (19.3718 -155.1873)
08/17 21:38:02 2.92md 0 km NNW of Indios, Puerto Rico (18.0000 -66.8228)
08/17 21:31:33 5.00mb south of the Fiji Islands (-23.1385 179.3199)
The magnitude reported is that which the U.S. Geological Survey considers official for this earthquake, and was the best available estimate of the earthquake's size, at the time that this page was created. Other magnitudes associated with web pages linked from here are those determined at various times following the earthquake with different types of seismic data. Although they are legitimate estimates of magnitude, the U.S. Geological Survey does not consider them to be the preferred "official" magnitude for the event.
Earthquake magnitude is a measure of the size of an earthquake at its source. It is a logarithmic measure. At the same distance from the earthquake, the amplitude of the seismic waves from which the magnitude is determined are approximately 10 times as large during a magnitude 5 earthquake as during a magnitude 4 earthquake. The total amount of energy released by the earthquake usually goes up by a larger factor: for many commonly used magnitude types, the total energy of an average earthquake goes up by a factor of approximately 32 for each unit increase in magnitude.
There are various ways that magnitude may be calculated from seismograms. Different methods are effective for different sizes of earthquakes and different distances between the earthquake source and the recording station. The various magnitude types are generally defined so as to yield magnitude values that agree to within a few-tenths of a magnitude-unit for earthquakes in a middle range of recorded-earthquake sizes, but the various magnitude-types may have values that differ by more than a magnitude-unit for very large and very small earthquakes as well as for some specific classes of seismic source. This is because earthquakes are commonly complex events that release energy over a wide range of frequencies and at varying amounts as the faulting or rupture process occurs. The various types of magnitude measure different aspects of the seismic radiation (e.g., low-frequency energy vs. high-frequency energy). The relationship among values of different magnitude types that are assigned to a particular seismic event may enable the seismologist to better understand the processes at the focus of the seismic event. The various magnitude-types are not all available at the same time for a particular earthquake.
Preliminary magnitudes based on incomplete but rapidly-available data are sometimes estimated and reported. For example, the Tsunami Warning Centers will calculate a preliminary magnitude and location for an event as soon as sufficient data are available to make an estimate. In this case, time is of the essence in order to broadcast a warning if tsunami waves are likely to be generated by the event. Such preliminary magnitudes are superseded by improved estimates of magnitude as more data become available.
For large earthquakes of the present era, the magnitude that is ultimately selected as the preferred magnitude for reporting to the public is commonly a moment magnitude that is based on the scalar seismic-moment of an earthquake determined by calculation of the seismic moment-tensor that best accounts for the character of the seismic waves generated by the earthquake. The scalar seismic-moment, a parameter of the seismic moment-tensor, can also be estimated via the multiplicative product rigidity of faulted rock x area of fault rupture x average fault displacement during the earthquake.
Magnitude Type, Magnitude Range, Distance Range, Equation
Mww (Moment W-phase)(generic notation Mw) ~5.0 and larger 1 - 90 degrees MW = 2/3 * (log10(MO) - 16.1),where MO is the seismic moment.
Note this is also unit-dependent; the formula above is for moment in dyne-cm. If using metric units (N.m), the constant is 9.1. Derived from a centroid moment tensor inversion of the W-phase (~50-2000 s; pass band based on size of EQ). Computed for all M5.0 or larger earthquakes worldwide, but generally robust for all M5.5 worldwide. Provides consistent results to M~4.5 within a regional network of high-quality broadband stations. Authoritative USGS magnitude if computed.
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Mwc (centroid) ~5.5 and larger 20 - 180 degrees MW = 2/3 * (log10(MO) - 16.1), where MO is the seismic moment.
Derived from a centroid moment tensor inversion of the long-period surface waves (~100-2000 s; pass band based on size of EQ). Generally computable for all M6.0 worldwide using primarily the Global Seismograph Network. Only authoritative if Mww is not computed, not published otherwise.
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Mwb (body wave) ~5.5 to ~7.0 30 - 90 degrees MW = 2/3 * (log10(MO) - 16.1), where MO is the seismic moment.
Derived from moment tensor inversion of long-period (~20-200 s; pass band based on size of EQ) body-waves (P- and SH). Generally computable for all M5.5 or larger events worldwide. Source complexity at larger magnitudes (~M7.5 or greater) generally limits applicability. Only authoritative if Mww and Mwc are not computed.
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Mwr (regional) ~4.0 to ~6.5 0 - 10 degrees MW = 2/3 * (log10(MO) - 16.1), where MO is the seismic moment.
Based on the scalar seismic-moment of the earthquake, derived from moment tensor inversion of the whole seismogram at regional distances (~10-100 s; pass band based on size of EQ). Source complexity and dimensions at larger magnitudes (~M7.0 or greater) generally limits applicability. Authoritative for <M5.0. Within the continental US and south-central Alaska where we have a large number of high quality broadband stations we expect we can compute an Mwr consistently for events as small as M4.0. In some areas of the country, with relatively dense broadband coverage, we can compute Mwr consistently to as small as M3.5.
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Ms20 or Ms (20sec surface wave) ~5.0 to ~8.5 20 - 160 degrees MS = log10 (A/T) 1.66 log10 (D) 3.30 .i
A magnitude based on the amplitude of Rayleigh surface waves measured at a period near 20 sec. Waveforms are shaped to the WWSSN LP response. Reported by NEIC, but rarely used as authoritative, since at these magnitudes there is almost always an Mw available. Ms is primarily valuable for large (>6), shallow events, providing secondary confirmation on their size. Ms_20 tends to saturate at about M8.3 or larger.
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mb (short-period body wave) ~4.0 to ~6.5 15 - 100 degrees mb = log10(A/T) Q(D,h) ,where A is the amplitude of ground motion (in microns); T is the corresponding period (in seconds); and Q(D,h) is a correction factor that is a function of distance, D(degrees), between epicenter and station and focal depth, h (in kilometers), of the earthquake.
Based on the amplitude of 1st arriving P-waves at periods of about 1 s. Waveforms are shaped to the WWSSN SP response. Reported for most M4.0-4.5 to 6.5 EQs that are observed teleseismically. Only authoritative for global seismicity for which there is no Mww, Mwc, Mwb or Mwr, typically 4.0-5.5 range. Mb tends to saturate at about M 6.5 or larger.
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Mfa (felt-area magnitude) any any various
An estimate of body-wave (mb) magnitude based on the size of the area over which the earthquake was felt, typically assigned to widely felt earthquakes that occurred before the invention of seismographs and to earthquakes occurring in the early decades of seismograph deployment for which magnitudes calculated from seismographic data are not available. The computations are based on isoseismal maps or defined felt areas using various intensity-magnitude or felt area-magnitude formulas. Reference: Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.
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ML Ml, or ml (local) ~2.0 to ~6.5 0 - 600 km
The original magnitude relationship defined by Richter and Gutenberg in 1935 for local earthquakes. It is based on the maximum amplitude of a seismogram recorded on a Wood-Anderson torsion seismograph. Although these instruments are no longer widely in use, ML values are calculated using modern instrumentation with appropriate adjustments. Reported by NEIC for all earthquakes in the US and Canada. Only authoritative for smaller events, typically M<4.0 for which there is no mb or moment magnitude. In the central and eastern United States, NEIC also computes ML, but restricts the distance range to 0-150 km. In that area it is only authoritative if there is no mb_Lg as well as no mb or moment magnitude.
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mb_Lg, mb_lg, or MLg (short-period surface wave) ~3.5 to ~7.0 150-1110 km (10 degres)
A magnitude for regional earthquakes based on the amplitude of the Lg surface waves as recorded on short-period instruments. Only authoritative for smaller events in the central and eastern United States, typically <4.0 for which there is no mb or moment magnitude.
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Md or md (duration) ~4 or smaller 0 - 400 km
Based on the duration of shaking as measured by the time decay of the amplitude of the seismogram. Sometimes the only magnitude available for very small events, but often used (especially in the past) to compute magnitude from seismograms with "clipped" waveforms due to limited dynamic recording range of analog instrumentation, which makes it impossible to measure peak amplitudes. Computed by NEIC but only published when there is no other magnitude available.
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Mi or Mwp (integrated p-wave) ~5.0 to ~8.0 all
Based on an estimate of moment calculated from the integral of the displacement of the P wave recorded on broadband instruments.
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Me (energy) ~3.5 and larger all Me = 2/3 log10E - 2.9,where E is the energy calculated by log10E = 11.8 1.5MS where energy, E, is expressed in ergs.
Based on the seismic energy radiated by the earthquake as estimated by integration of digital waveforms.
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Mh any any N/A
Non-standard magnitude method. Generally used when standard methods will not work. Sometimes use as a temporary designation until the magnitude is finalized.
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Finite Fault Modeling ~7.0 and larger 30 - 90 degrees
FFM modeling provides a kinematic description of faulting including estimates of maximum slip, area of rupture and moment release as a function of time. Results are used to provide constraints on fault dimensions and slip used in damage assessment modeling (ShakeMap, PAGER) and to model stress changes (Coulomb stress modeling) on the active fault and/or adjacent faults.
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Mint (intensity magnitude) any any various
A magnitude estimated from the maximum reported intensity, typically for earthquakes occurring before seismic instruments were in general use. This has been used for events where the felt reports were from too few places to use a magnitude determined from a felt area. Reference: Catalog of Hawaiian earthquakes, 1823-1959, by Fred W. Klein and Thomas L. Wright U.S. Geological Survey Professional Paper 1623, USGS Information Services, Denver: 2000.
