In connection with earthquakes, syzygy refers to the idea that the combined tidal effects of the sun and moon – either directly as earth tides in the crust itself, or indirectly by hydrostatic loading due to ocean tides[2] – should be able to trigger earthquakes in rock that is already stressed to the point of fracturing, and therefore a higher proportion of earthquakes should occur at times of maximal tidal stress, such as at the new and full moons.
Previously, scientists have searched for such a correlation for over a century, but with the exception of volcanic areas (including mid-ocean spreading ridges)[3] the results have been mixed.[4] It has been suggested that some negative results are due to failure to account for tidal phase and fault orientation (dip),[5] while "many studies reporting positive correlations suffer from a lack of statistical rigor."[6] One systematic investigation found "no evidence for an increase in seismicity during intervals of large tidal range but there is clear evidence for small but significant increase in earthquake rates near low tide"; it did not find an increase of earthquakes near peak spring tides.[7] Seismicity is favored at low tides, particularly for reverse faults, because unloading unclamps the fault, reducing friction. Ocean loading has no effect at all on strike-slip faults.[8]
Research work has shown a robust correlation between small tidally induced forces and non-volcanic tremor activity.[9] Volcanologists use the regular, predictable Earth tide movements to calibrate and test sensitive volcano deformation monitoring instruments. The tides may also trigger volcanic events. [10][11]
Sottili, G.; Martino, S.; Palladino, D.M.; Paciello, A.; Bozzano, F. (2007), "Effects of tidal stresses on volcanic activity at Mount Etna, Italy", Geophysical Research Letters, 34 (L01311), Bibcode:2007GeoRL..34.1311S, doi:10.1029/2006GL028190.
An earthquake – also called a quake, tremor, or temblor – is the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume.
A tsunami is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are in turn generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water from a large event.
Induced seismicity is typically earthquakes and tremors that are caused by human activity that alters the stresses and strains on Earth's crust. Most induced seismicity is of a low magnitude. A few sites regularly have larger quakes, such as The Geysers geothermal plant in California which averaged two M4 events and 15 M3 events every year from 2004 to 2009. The Human-Induced Earthquake Database (HiQuake) documents all reported cases of induced seismicity proposed on scientific grounds and is the most complete compilation of its kind.
A volcano tectonic earthquake or volcano earthquake is caused by the movement of magma beneath the surface of the Earth. The movement results in pressure changes where the rock around the magma has a change in stress. At some point, this stress can cause the rock to break or move. This seismic activity is used by scientists to monitor volcanoes. The earthquakes may also be related to dike intrusion and/or occur as earthquake swarms. Usually they are characterised by high seismic frequency and lack the pattern of a main shock followed by a decaying aftershock distribution of fault related tectonic earthquakes.
The Cascadia subduction zone is a 960 km (600 mi) fault at a convergent plate boundary, about 100–200 km (70–100 mi) off the Pacific coast, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30 m (98 ft). The Oregon Department of Emergency Management estimates shaking would last 5–7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American plate. The zone varies in width and lies offshore beginning near Cape Mendocino, Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.
A harmonic tremor is a sustained release of seismic and infrasonic energy typically associated with the underground movement of magma, the venting of volcanic gases from magma, or both in volcanoes, and with repetitive stick-slip or other impulsive activity in non-volcanic systems. It is a long-duration release of seismic energy, often containing distinct spectral lines. Volcanic tremor often precedes or accompanies a volcanic eruption. Being a long-duration continuous signal from a temporally extended source tremor contrasts distinctly with transient and often impulsive sources of seismic radiation typically associated with earthquakes and explosions.
Coulomb stress transfer is a seismic-related geological process of stress changes to surrounding material caused by local discrete deformation events. Using mapped displacements of the Earth's surface during earthquakes, the computed Coulomb stress changes suggest that the stress relieved during an earthquake not only dissipates but can also move up and down fault segments, concentrating and promoting subsequent tremors. Importantly, Coulomb stress changes have been applied to earthquake-forecasting models that have been used to assess potential hazards related to earthquake activity.
James O. Berkland was an American geologist who controversially claimed to be able to predict earthquakes, including the 1989 Loma Prieta earthquake and 1994 Northridge Earthquake and who popularized the idea that some people are earthquake sensitive. He was profiled in a popular 2006 book as The Man Who Predicts Earthquakes. The book includes a chapter that notes "Many of Berkland's theories--based on tides, moons, disoriented pets, lost cats and dogs, and magnetic field changes--were factors in the great Indian Ocean quake-tsunami disaster on December 26, 2004." but neither his methods nor his predictions have been published in any scientific journals for peer review. His results have been disputed by peers, with other scientists going so far as calling him a crank and a clown.
Remotely triggered earthquakes are a result of the effects of large earthquakes at considerable distance, outside of the immediate aftershock zone. The farther one gets from the initiating earthquake in both space and time, the more difficult it is to establish an association.
A slow earthquake is a discontinuous, earthquake-like event that releases energy over a period of hours to months, rather than the seconds to minutes characteristic of a typical earthquake. First detected using long term strain measurements, most slow earthquakes now appear to be accompanied by fluid flow and related tremor, which can be detected and approximately located using seismometer data filtered appropriately. That is, they are quiet compared to a regular earthquake, but not "silent" as described in the past.
The 2007 Bengkulu earthquakes were a series of megathrust earthquakes that struck the Sunda Trench off the coast of Sumatra, Indonesia, with three of magnitude 7 or greater. A series of tsunami bulletins was issued for the area. The most powerful of the series had a magnitude of 8.4, which makes it in the top 20 of the largest earthquakes ever recorded on a seismograph.
Episodic tremor and slip (ETS) is a seismological phenomenon observed in some subduction zones that is characterized by non-earthquake seismic rumbling, or tremor, and slow slip along the plate interface. Slow slip events are distinguished from earthquakes by their propagation speed and focus. In slow slip events, there is an apparent reversal of crustal motion, although the fault motion remains consistent with the direction of subduction. ETS events themselves are imperceptible to human beings and do not cause damage.
The 1995 Antofagasta earthquake occurred on July 30 at 05:11 UTC with a moment magnitude of 8.0 and a maximum Mercalli intensity of VII. The Antofagasta Region in Chile was affected by a moderate tsunami, with three people killed, 58 or 59 injured, and around 600 homeless. Total damage from the earthquake and tsunami amounted to $1.791 million.
The 1868 Hawaiʻi earthquake was the largest recorded in the history of Hawaiʻi island, with an estimated magnitude of 7.9 Mfa and a maximum Mercalli intensity of X (Extreme). The earthquake occurred at 4 p.m. local time on April 2, 1868, and caused a landslide and tsunami that led to 77 deaths. The aftershock sequence for this event has continued up to the present day.
The 2012 Indian Ocean earthquakes were magnitude 8.6 and 8.2 Mw undersea earthquakes that struck near the Indonesian province of Aceh on 11 April at 15:38 local time. Initially, authorities feared that the initial earthquake would cause a tsunami and warnings were issued across the Indian Ocean; however, these warnings were subsequently cancelled. These were unusually strong intraplate earthquakes and the largest strike-slip earthquake ever recorded.
This is a list of different types of earthquake.
Earthquake weather is a type of weather popularly believed to precede earthquakes.
The 1930 Pyu earthquake occurred on December 4 at 01:21 local time. The epicenter was located north to Bago, Burma, then part of British India. The magnitude of the earthquake was estimated at Mw 7.3, or Ms 7.3.
The 1956 Amorgos earthquake occurred at 03:11 UTC on July 9. It had a magnitude of 7.7 on the moment magnitude scale and a maximum perceived intensity of IX on the Mercalli intensity scale. The epicentre was to the south of the island of Amorgos, the easternmost island of the Cyclades in the Aegean Sea. There was significant damage on Amorgos and the neighbouring island of Santorini. It was the largest earthquake in Greece in the 20th century. It was followed 13 minutes later by a magnitude 7.2 earthquake near Santorini. It triggered a major tsunami with a maximum run-up of 30 m. The combined effects of the earthquake shaking and the tsunami caused the deaths of 53 people with a further 100 injured.
The 1852 Banda Sea earthquake struck on 26 November at 07:40 local time, affecting coastal communities on the Banda Islands. It caused violent shaking lasting five minutes, and was assigned XI on the Modified Mercalli intensity scale in the Maluku Islands. A tsunami measuring up to 8 m (26 ft) slammed into the islands of Banda Neira, Saparua, Haruku and Ceram. The tsunami caused major damage, washing away many villages, ships and residents. At least 60 people were killed in the earthquake and tsunami. The earthquake had an estimated moment magnitude of 7.5 or 8.4–8.8, according to various academic studies.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
