💾 Archived View for federal.cx › earthquake.gmi captured on 2023-01-29 at 03:38:03. 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)
01/29 03:29:26 1.90ml 67 km WNW of Beluga, Alaska (61.3991 -152.2122)
01/29 03:20:21 4.50mb 167 km NW of Tobelo, Indonesia (2.8217 126.9677)
01/29 02:57:55 2.70ml 50 km E of Port Alsworth, Alaska (60.1321 -153.4253)
01/29 02:57:54 2.40ml 11 km ENE of Halibut Cove, Alaska (59.6433 -151.0389)
01/29 02:27:58 1.90ml 37 km ESE of Denali Park, Alaska (63.5974 -148.2100)
01/29 01:55:26 2.52ml 9 km NE of Pāhala, Hawaii (19.2492 -155.4067)
01/29 01:54:03 2.54md 1 km SSW of Maria Antonia, Puerto Rico (17.9657 -66.8943)
01/29 01:45:44 4.60mb Molucca Sea (2.8834 126.7959)
01/29 01:26:53 2.33md 17km NW of Alder Springs, CA (39.7572 -122.8675)
01/29 00:52:21 2.05md 6km NW of The Geysers, CA (38.8158 -122.7953)
01/29 00:00:51 1.72md 6km WNW of The Geysers, CA (38.8015 -122.8187)
01/28 23:58:56 2.33md 5 km SSW of Pāhala, Hawaii (19.1572 -155.4885)
01/28 23:56:58 3.70mw 12km WSW of Ferndale, CA (40.5355 -124.3973)
01/28 23:38:29 2.00ml 34 km WSW of Karluk, Alaska (57.4463 -154.9881)
01/28 22:14:41 2.01md 1 km ENE of Pāhala, Hawaii (19.2098 -155.4635)
01/28 22:07:26 2.20ml 45 km NW of Toyah, Texas (31.6198 -104.1149)
01/28 21:02:51 2.10ml 46 km S of Ugashik, Alaska (57.0967 -157.3975)
01/28 20:57:31 2.50ml 35 km SE of Mina, Nevada (38.1726 -117.8079)
01/28 20:42:35 2.30ml Central Alaska (63.6192 -148.2019)
01/28 20:38:01 2.07md 2km NNE of The Geysers, CA (38.7953 -122.7423)
01/28 20:18:21 1.83md 3km S of Cobb, CA (38.7943 -122.7243)
01/28 20:16:54 3.44md 124 km N of Brenas, Puerto Rico (19.5878 -66.3143)
01/28 20:09:58 4.50mb 12 km WSW of Khowy, Iran (38.5084 44.8234)
01/28 19:15:54 3.30ml 35 km WSW of Skwentna, Alaska (61.8965 -152.0512)
01/28 19:15:18 5.30mww 33 km NE of Tobelo, Indonesia (1.9422 128.2275)
01/28 19:11:57 2.02md 9 km ENE of Pāhala, Hawaii (19.2312 -155.3883)
01/28 18:49:17 2.02md 14 km ESE of Pāhala, Hawaii (19.1758 -155.3462)
01/28 18:43:50 1.92md 9 km SSW of Pāhala, Hawaii (19.1170 -155.4983)
01/28 18:14:44 5.90mww 14 km SSW of Khowy, Iran (38.4246 44.8991)
01/28 17:41:05 2.90ml 25 km SSW of King Salmon, Alaska (58.4775 -156.8404)
01/28 17:35:55 4.70mb 100 km SW of Paratunka, Russia (52.2371 157.3806)
01/28 17:16:15 3.70ml Nevada (38.1734 -117.8643)
01/28 17:00:21 1.80ml 32 km SSW of Petersville, Alaska (62.2380 -151.0374)
01/28 16:10:51 4.00mb 194 km W of Tofino, Canada (48.9990 -128.5592)
01/28 15:47:55 5.10mb Banda Sea (-6.5211 129.8374)
01/28 14:44:30 2.55ml 16 km SSE of Pāhala, Hawaii (19.0628 -155.4212)
01/28 13:53:09 4.60mb 26 km SSE of Mandalī, Iraq (33.5453 45.6996)
01/28 13:22:50 2.63ml 17 km E of Naalehu, Hawaii (19.0463 -155.4117)
01/28 11:58:29 4.50mb 23 km NE of Cañaveral, Peru (-3.7951 -80.4995)
01/28 11:55:35 2.00ml 42 km SE of Port Graham, Alaska (59.0638 -151.3401)
01/28 11:54:07 2.16ml 12 km S of Fern Forest, Hawaii (19.3570 -155.1240)
01/28 11:50:25 2.90ml 116 km SW of Hydaburg, Alaska (54.5277 -134.2098)
01/28 11:24:09 1.74md 4km WNW of Mammoth Lakes, CA (37.6537 -119.0182)
01/28 10:21:52 2.60ml 64 km WNW of False Pass, Alaska (55.0991 -164.3183)
01/28 10:03:40 2.09md 13 km ESE of Pāhala, Hawaii (19.1385 -155.3698)
01/28 09:39:51 2.60ml 53 km S of Ugashik, Alaska (57.0365 -157.3527)
01/28 09:39:50 2.88ml 8 km SW of Corinne, Utah (41.4968 -112.1745)
01/28 09:32:40 2.50ml 9 km NE of Dry Creek, Alaska (63.7164 -144.5397)
01/28 09:13:23 5.30mb Southwest Indian Ridge (-34.8219 54.3574)
01/28 09:09:44 1.77md Virginia-North Carolina border region (36.3188 -81.4702)
01/28 08:11:30 2.28md 2 km WSW of Indios, Puerto Rico (17.9842 -66.8363)
01/28 08:06:15 1.92ml 21km W of Delta, B.C., MX (32.3720 -115.4183)
01/28 07:09:06 2.02ml 7km NE of Banning, CA (33.9778 -116.8282)
01/28 06:05:20 3.10ml Southern Alaska (61.7273 -151.5991)
01/28 05:42:51 3.00ml 3 km N of Breñón, Panama (8.6615 -82.8114)
01/28 05:33:02 3.32md Puerto Rico region (17.9850 -66.8852)
01/28 05:32:49 4.30mb 2 km SSE of Pinarella, Italy (44.2240 12.3869)
01/28 05:28:36 2.23ml 10km NNW of Anza, CA (33.6397 -116.7183)
01/28 05:02:34 5.00mb 82 km ESE of Yigo Village, Guam (13.1645 145.5474)
01/28 04:59:29 1.74md 9 km E of Pāhala, Hawaii (19.2115 -155.3913)
01/28 04:52:36 3.51ml 3 km SW of Dibble, Oklahoma (35.0087 -97.6616)
01/28 03:58:06 1.80ml 60 km SW of Skwentna, Alaska (61.5491 -152.0667)
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.
