View Full Version : Are earthquakes triggered by lunar/solar tides? new info

Roger E. Moore
2018-Sep-06, 09:42 PM

Influence of Tidal Forces on the Triggering of Seismic Events

Varga, Péter; Grafarend, Erik

Tidal stresses are generated in any three-dimensional body influenced by an external inhomogeneous gravity field of rotating planets or moons. In this paper, as a special case, stresses caused within the solid Earth by the body tides are discussed from viewpoint of their influence on seismic activity. The earthquake triggering effects of the Moon and Sun are usually investigated by statistical comparison of tidal variations and temporal distribution of earthquake activity, or with the use of mathematical or experimental modelling of physical processes in earthquake prone structures. In this study, the magnitude of the lunisolar stress tensor in terms of its components along the latitude of the spherical surface of the Earth as well as inside the Earth (up to the core-mantle boundary) were calculated for the PREM (Dziewonski and Anderson in Phys Earth Planet Inter 25(4):297-356, 1981). Results of calculations prove that stress increases as a function of depth reaching a value around some kPa at the depth of 900-1500 km, well below the zone of deep earthquakes. At the depth of the overwhelming part of seismic energy accumulation (around 50 km) the stresses of lunisolar origin are only (0.0-1.0)ˇ103 Pa. Despite the fact that these values are much smaller than the earthquake stress drops (1-30 MPa) (Kanamori in Annu Rev Earth Planet Sci 22:207-237, 1994) this does not exclude the possibility of an impact of tidal forces on outbreak of seismic events. Since the tidal potential and its derivatives are coordinate dependent and the zonal, tesseral and sectorial tides have different distributions from the surface down to the CMB, the lunisolar stress cannot influence the break-out of every seismological event in the same degree. The influencing lunisolar effect of the solid earth tides on earthquake occurrences is connected first of all with stress components acting parallel to the surface of the Earth. The influence of load tides is limited to the loaded area and its immediate vicinity.



Investigation of the relationship between rock strain and radon concentration in the tidal frequency-range

Mentes, Gyula

Changes in the radon gas concentration can precede geodynamic processes associated with tectonic, volcanic activities and earthquakes. For this reason the relationship between rock strain and radon concentration is an important scientific issue to be answered. According to the complexity of the radon emanation process influenced by environmental effects, the interpretation of radon concentration variation as a possible precursor of geodynamic processes is not yet resolved unambiguously. The Sopronbánfalva Geodynamic Observatory in Hungary is one of the few places where radon concentration and rock strain variations are simultaneously monitored. The object of this study is to investigate the connection between indoor radon concentration and rock strain in the tidal frequency-range on the basis of seven-year long data series measured in years from 2009 till 2015. The relationship between rock deformation and radon concentration was investigated together with the temperature and barometric pressure effects. It was found that the strain induced radon concentration variations are in the order of 10-100 Bq nstr-1, while the concentration variations bear more considerable similarity and relation to the temperature and barometric variations. The theoretical tide at the location of the measurement site and tidal components computed from strain, radon concentration, barometric pressure and temperature data were compared with each other. Spectral and tidal analysis of data demonstrated that only the thermally induced solar components S1 and S2 are present in the radon concentration but their amplitudes hardly exceed the spectral noise level. The principal lunar semidiurnal M2 and diurnal O1 tidal waves cause the largest rock strain variations. The lack of the O1 and M2 constituents in the radon concentration confirms the fact that the detected S1 and S2 tidal components appear due to the barometric tide and the daily variations of the temperature and barometric pressure.



Earthquake potential revealed by tidal influence on earthquake size-frequency statistics

Ide, Satoshi; Yabe, Suguru; Tanaka, Yoshiyuki

The possibility that tidal stress can trigger earthquakes is long debated. In particular, a clear causal relationship between small earthquakes and the phase of tidal stress is elusive. However, tectonic tremors deep within subduction zones are highly sensitive to tidal stress levels, with tremor rate increasing at an exponential rate with rising tidal stress. Thus, slow deformation and the possibility of earthquakes at subduction plate boundaries may be enhanced during periods of large tidal stress. Here we calculate the tidal stress history, and specifically the amplitude of tidal stress, on a fault plane in the two weeks before large earthquakes globally, based on data from the global, Japanese, and Californian earthquake catalogues. We find that very large earthquakes, including the 2004 Sumatran, 2010 Maule earthquake in Chile and the 2011 Tohoku-Oki earthquake in Japan, tend to occur near the time of maximum tidal stress amplitude. This tendency is not obvious for small earthquakes. However, we also find that the fraction of large earthquakes increases (the b-value of the Gutenberg-Richter relation decreases) as the amplitude of tidal shear stress increases. The relationship is also reasonable, considering the well-known relationship between stress and the b-value. This suggests that the probability of a tiny rock failure expanding to a gigantic rupture increases with increasing tidal stress levels. We conclude that large earthquakes are more probable during periods of high tidal stress.

John Mendenhall
2018-Sep-06, 10:58 PM
There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
— Mark Twain, Life on the Mississippi (1883)

Your own tag line.

2018-Sep-07, 01:29 AM
It seems to make sense that this could be true. After all, it makes sense that there would be a relationship between tidal stress and earthquakes. However, it doesn't really do much of practical importance, because I think the times of maximum stress happen maybe twice a day, and it would be silly to evacuate homes and buildings twice every day just in the small chance that a big earthquake might happen.

2018-Sep-07, 06:35 AM
it seems to me that tidal effects reduce the chance of big earthquakes. If we consider the very slow movement of tectonic plates which causes stress in the slip zones, that stress accumulates equally slowly. The regular tidal triggers would cause small slips regularly while if they were absent the stress might just increase until a major failure occurs. I am reminded of an analog in controlling large forces in a big ship. Analysis of accumulated hysteresis suggests the system will be very jerky but the relatively minor vibration from the engines allows very precise control. In that analogy it is a statistically reliable effect.

Roger E. Moore
2018-Sep-07, 12:12 PM
I neglected to add my own thoughts when I posted the above. I admit I was impressed by the idea of measuring radon release as a sign of rock strain.

The idea that tides might affect earthquakes is an old one, and SF picked up on it with the publication of When Worlds Collide in the early 20th century (and in the later movie). To actually see evidence for it, though, is pleasing.

Roger E. Moore
2018-Nov-16, 08:06 PM
A paper out recently describing earthquakes and similar phenomena on tidally locked worlds. Interesting reading in light of the current topic here.


Seismicity on Tidally Active Solid-Surface Worlds

T.A. Hurford, et al. (Submitted on 15 Nov 2018)

Tidal interactions between planets or stars and the bodies that orbit them dissipate energy in their interiors. The energy dissipated drives internal heating and a fraction of that energy will be released as seismic energy. Here we formalize a model to describe the tidally-driven seismic activity on planetary bodies based on tidal dissipation.

2018-Nov-17, 12:21 AM
I've been watching Iceland (https://en.vedur.is/earthquakes-and-volcanism/earthquakes/) for about 10 years now.
Never seen any obvious correlation between moon phase and earthquakes.
As far as I can tell, there's no 14 or 28.whatever day correlation with between tide and quake.