💾 Archived View for federal.cx › earthquake.gmi captured on 2022-04-28 at 17:51:16. 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)
04/28 21:20:33 1.83ml 44km NE of Holtville, CA (33.0512 -114.9992)
04/28 21:08:16 2.10ml 20 km ESE of Denali National Park, Alaska (63.4897 -151.3252)
04/28 19:48:53 2.00ml 93 km NNW of Rachel, Nevada (38.4011 -116.2021)
04/28 19:42:33 2.08md 5 km NNW of Sabana Grande, Puerto Rico (18.1192 -66.9842)
04/28 19:42:10 4.40mb 91 km ENE of Shikotan, Russia (44.0827 147.7965)
04/28 19:24:07 2.54md 5 km SSE of Maria Antonia, Puerto Rico (17.9297 -66.8722)
04/28 19:14:47 1.90ml 53 km N of Petersville, Alaska (62.9785 -150.7921)
04/28 19:07:12 2.21md 7km ENE of Bonadelle Ranchos-Madera Ranchos, CA (37.0173 -119.8113)
04/28 17:30:13 2.14md 2 km SSW of Pāhala, Hawaii (19.1822 -155.4888)
04/28 17:08:58 4.10ml 36 km WSW of Mentone, Texas (31.6120 -103.9696)
04/28 16:36:56 1.90ml 59 km WNW of Ninilchik, Alaska (60.1843 -152.7117)
04/28 16:18:44 4.20mb 106 km SW of Uyuni, Bolivia (-21.2380 -67.4296)
04/28 16:04:26 3.10ml 271 km SE of Chiniak, Alaska (56.2667 -148.5584)
04/28 15:43:23 1.80md 5 km SW of Fuig, Puerto Rico (17.9595 -66.9587)
04/28 15:00:01 3.30ml 23 km NNE of Hawthorne, Nevada (38.7001 -118.4791)
04/28 14:52:57 2.40ml 5 km S of Pāhala, Hawaii (19.1547 -155.4740)
04/28 14:52:28 2.40ml 118 km WNW of Yakutat, Alaska (60.1185 -141.5037)
04/28 13:54:43 2.01md 8 km ENE of Pāhala, Hawaii (19.2273 -155.4045)
04/28 13:44:54 1.76ml 12km E of Coso Junction, CA (36.0338 -117.8135)
04/28 13:42:16 2.20ml 12km E of Coso Junction, CA (36.0323 -117.8138)
04/28 13:23:13 1.82ml 8km WSW of Grapevine, CA (34.9170 -119.0095)
04/28 13:21:13 6.00mww 175 km NNE of Madang, Papua New Guinea (-3.8986 146.6605)
04/28 12:54:28 4.90mb 159 km NE of Madang, Papua New Guinea (-4.0700 146.6536)
04/28 12:32:07 2.00ml 56 km ENE of Pedro Bay, Alaska (60.0198 -153.2061)
04/28 12:23:46 1.89ml 7 km ENE of Kenilworth, Utah (39.7057 -110.7202)
04/28 12:18:12 1.97md 10km N of French Gulch, CA (40.7980 -122.6445)
04/28 12:10:03 2.13md 6 km S of Pāhala, Hawaii (19.1408 -155.4782)
04/28 12:05:53 1.94ml 7km S of Lucerne Valley, CA (34.3830 -116.9768)
04/28 11:51:06 1.79md 10km NNE of Cloverdale, CA (38.8912 -122.9937)
04/28 11:42:28 5.00mww 9 km NNE of Pilar, Philippines (9.9399 126.1337)
04/28 11:11:55 2.02md 10km ESE of Gilroy, CA (36.9782 -121.4648)
04/28 10:58:13 2.20ml 154 km SE of Akutan, Alaska (53.2078 -164.0352)
04/28 10:34:18 2.66md 9km N of French Gulch, CA (40.7880 -122.6485)
04/28 10:25:40 2.24md 5 km ENE of La Parguera, Puerto Rico (17.9888 -66.9943)
04/28 10:22:36 2.46ml 12km SSW of Big Bear Lake, CA (34.1397 -116.9565)
04/28 10:12:51 2.21md 6 km NE of La Parguera, Puerto Rico (18.0097 -66.9985)
04/28 10:03:21 4.70mb 89 km E of Mutsu, Japan (41.2195 142.2820)
04/28 09:29:17 4.40mb 81 km SE of Isangel, Vanuatu (-19.9753 169.9052)
04/28 09:11:32 2.40md 1 km SE of Indios, Puerto Rico (17.9873 -66.8122)
04/28 08:25:37 1.94ml 11 km E of Hebgen Lake Estates, Montana (44.7867 -111.0428)
04/28 08:22:38 2.80ml 47 km W of Mentone, Texas (31.7393 -104.0968)
04/28 07:57:56 4.30mb 6 km S of Lloró, Colombia (5.4386 -76.5392)
04/28 07:31:16 2.10ml 29 km NNE of Bondurant, Wyoming (43.4545 -110.2925)
04/28 07:30:56 2.53md 5km NNE of Pinnacles, CA (36.5718 -121.1160)
04/28 07:20:44 3.58md 71 km NNE of Punta Cana, Dominican Republic (19.1290 -68.0493)
04/28 06:56:55 2.80ml 62 km NE of Arctic Village, Alaska (68.5535 -144.5628)
04/28 06:46:51 4.70mb 13 km SSW of Hihifo, Tonga (-16.0568 -173.8581)
04/28 06:31:33 2.37md 6 km WSW of Pole Ojea, Puerto Rico (17.9513 -67.2412)
04/28 06:21:07 2.21ml 28 km NNE of Bondurant, Wyoming (43.4453 -110.2872)
04/28 06:18:27 1.80ml 69 km ENE of Pedro Bay, Alaska (60.1234 -153.0687)
04/28 06:11:38 2.09md 3 km SSW of Indios, Puerto Rico (17.9638 -66.8278)
04/28 05:41:34 1.90ml 60 km ENE of Pedro Bay, Alaska (60.0590 -153.1703)
04/28 05:27:11 1.85ml 22km SW of Maricopa, CA (34.9133 -119.5632)
04/28 05:18:06 1.76ml 20km E of Little Lake, CA (35.9470 -117.6860)
04/28 05:14:39 2.53md 3 km WSW of Indios, Puerto Rico (17.9800 -66.8527)
04/28 05:14:05 4.10mb 145 km ESE of Iquique, Chile (-20.8154 -68.9117)
04/28 04:37:06 2.20ml 99 km NE of Ouzinkie, Alaska (58.4686 -151.1619)
04/28 04:32:22 2.99ml 24km S of Kettleman City, CA (35.7945 -119.9882)
04/28 04:21:58 3.00ml 37 km NNW of Toyah, Texas (31.6090 -103.9935)
04/28 04:14:56 4.50mb 61 km NNW of Atka, Alaska (52.7174 -174.5199)
04/28 04:10:58 3.70ml 37 km NNW of Toyah, Texas (31.6120 -103.9798)
04/28 04:07:35 2.90ml 38 km NNW of Toyah, Texas (31.6161 -103.9901)
04/28 03:49:11 2.90ml 116 km E of Chignik, Alaska (56.3537 -156.5204)
04/28 03:48:34 2.35ml 7 km ENE of Fall City, Washington (47.6030 -121.8053)
04/28 03:35:24 1.99md 9 km ENE of Pāhala, Hawaii (19.2303 -155.3972)
04/28 03:33:39 5.20ml 118 km E of Chignik, Alaska (56.3596 -156.4956)
04/28 02:46:07 2.11md 24km S of Kettleman City, CA (35.7918 -120.0022)
04/28 02:37:21 1.75ml 6km SSE of Brawley, CA (32.9252 -115.5148)
04/28 02:27:39 1.82md 3 km SSW of Pāhala, Hawaii (19.1718 -155.4895)
04/28 02:22:41 3.03md 9 km S of Guánica, Puerto Rico (17.8847 -66.8912)
04/28 01:54:13 1.94md 10 km ENE of Pāhala, Hawaii (19.2250 -155.3863)
04/28 01:52:44 2.54md 5km NNE of Pinnacles, CA (36.5730 -121.1268)
04/28 01:44:08 3.30ml 55 km S of Whites City, New Mexico (31.6721 -104.4116)
04/28 01:23:43 4.70mb 34 km SSW of Shimo-furano, Japan (43.0556 142.2621)
04/28 01:13:05 2.31ml 4 km SSW of Pāhala, Hawaii (19.1677 -155.4948)
04/28 00:07:30 2.24ml 25 km NW of Stanley, Idaho (44.3562 -115.1887)
04/28 00:01:07 4.80mb 117 km SSE of Amahai, Indonesia (-4.3683 129.1707)
04/27 23:25:07 1.74ml 28 km NNE of Bondurant, Wyoming (43.4465 -110.2842)
04/27 23:09:23 5.40mww 182 km N of Wé, New Caledonia (-19.2902 167.5419)
04/27 22:35:55 2.17md 5 km S of Pāhala, Hawaii (19.1527 -155.4837)
04/27 22:19:53 1.88ml 6 km SSW of Volcano, Hawaii (19.3875 -155.2495)
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.
