Tilts, global tectonics and earthquake prediction

Journal of Geodynamics, 2006

The horizontal pendulums of the Grotta Gigante (Giant Cave) in the Trieste Karst, are long-base tiltmeters with Zöllner type suspension. The instruments have been continuously recording tilt and shear in the Grotta Gigante since the date of their installation by Prof. Antonio Marussi in 1966. Their setup has been completely overhauled several times since installation, restricting the interruptions of the measurements though to a minimum. The continuous recordings, apart from some interruptions, cover thus almost 40 years of measurements, producing a very noticeable long-term tiltmeter record of crustal deformation. The original recording system, still in function, was photographic with a mechanical timing and paper-advancing system, which has never given any problems at all, as it is very stable and not vulnerable by external factors as high humidity, problems in power supply, lightning or similar. In December 2003 a new recording system was installed, based on a solid-state acquisition system intercepting a laser light reflected from a mirror mounted on the horizontal pendulum beam. The sampling rate is 30 Hz, which turns the long-base instrument to a very-broad-band tiltmeter, apt to record the tilt signal on a broad-band of frequencies, ranging from secular deformation rate through the earth tides to seismic waves. Here we describe the acquisition system and present two endline members of the instrumental observation, the up to date long-term recording, and the observation of the great Sumatra-Andaman Islands earthquake of December 26, 2004, seismic moment magnitude Mw = 9.1–9.3 [Lay, T., Kanamori, H., Ammon, C.J., Nettles, M., Ward, S.N., Aster, R.C., Beck, S.L., Bilek, S.L., Brudzinski, M.L., Butler, R., DeShon, H.R., Ekström, G., Satake, K., Sipkin, S., 2005. The Great Sumatra-Andaman Earthquake of 26 December 2004. Science. 308, 1127–1133.]. The secular-term observations indicate an average tilting over the last four decades towards NW of 23.4 nrad/year. We find evidences that this tilting is regional and has been going on since at least 125 ka. The recent earthquake of December 26, 2004 was well recorded by the pendulums. We show that the free oscillation modes were activated, including the lowest modes as e.g. 0T2, 0T3, 0T4, 0T5 and 2S1, 0S3, 0S4, 1S2.

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1973

Three borehole installation of 15 s horizontal pendulums (of the Lamont lunar type) with capacitance displacement transducers were carried out in 1968-1969 in Central Alaska in Gilmore (GLM near Fairbanks), Patson (PAT) and McKinley (MCK) int he Alaska Range. Data are telemetered over phone lines and v.h.f. radio links and the sensitivity is better than 10~9 rad/m m of chart recording. Tilt steps similar to strain steps have been observed for earthquakes with magnitude from 2 to 8 and distances ranging from 10 to 9000 km. The tilt step propagation velocity from the hypocentre to the station increases from about 1.3 km/s near the epicentral area to 2.6 to 2.8 km/s at 60 to 80 km and to 3.1 km/s at teleseismic distances. Tilt directions, amplitudes and velocities observed at several stations simultaneously for the same earthquake are internally consistent. For local Fairbanks quakes the data from the Alaska long period array (ALPA) also have been used and span a full quadrant from the...

Strain and tilt precursors to earthquakes are unconvincing because they are rarely reported from more than one instrument, and because anomalous strains and tilts can result from instrumental artifacts or near-surface hydrology etc. The article makes a case that real strain and tilt precursors, if they exist, might be expected to be observed with a delay relative to the earthquake preparation process, due to the propensity for surface strain meters and tilt meters to be installed in competent materials, between compliant zones where strains may be concentrated.

International Geophysics, 2002

Greenwich _ Meridian Euler vector , ,,, ,~P" O312 Euler pole FIGURE 2 Geometry of plate motions. At any point r along the boundary between plate i and plate j, with geopraphic latitude )~ and longitude #, the linear velocity of plate j with respect to plate i is vii =o)ji • r. The Euler pole at latitude 0 and longitude 4) is the intersection of the Euler vector o)ji with the Earth's surface.

Geodesy and Geodynamics, 2010

The global plate motion rates n are not uniform in time and space. The rotation rates were larger than 0. 545 ° /Ma for Cocos, Philippine Sea, Pacific, Nazca, Australia, India and Arabia plates, but smaller than 0. 315° /Ma. for other plates. Compared to 1997. 0, the fi values of the three oceanic plates in 2000. 0 increased by ,respectively ,2. 4% ,2. 1% and 41. 7%, and the northward movement rates of the the India plate and western part of the Australia plate increased by 3. 38 mml a on the average. The spatial distribution of earthquakes was dependent on earthquake magnitude. Earthquakes of 5. 0 ~Mw < 7. 0 were located mainly in plate-margin zones and intra-plate crustal deformation zones joining the southern margin of Eurasia plate. Earthquakes of Mw ~ 7. 0 concentrated basically in the circum-Pacific and South Asia zones, but hardly in midocean-ridge seismic zones. Earthquakes of Mw~8. 0 were located only in the margin zones of the lndia,Australia,Pacific and Nazca plates orthogonal to the direction of plate motion. Compared with previous eighteen years ,global earthquake activity enhanced obviously after 1994' especially after 2001. The n value of a plate was closely related to the activity of strong earthquakes. The largest earthquakes were located in the front-margin zones of plates having the largest fi values. Energy released by strong earthquakes comes mainly from kinetic energy of the plates. Global seismicity enhancement was caused mainly by the acceleration of the three oceanic plates. Larger enhancement of global earthquake activity lagged behind the movement acceleration of the three oceanic plates by four years.

2008

The motion of a point is specified completely by its six components: three translations and three rotations. Traditionally, only the translational components of the earthquake ground shaking and structural response have been recorded. In part, the absence of direct observations of rotational motions resulted from lack of inexpensive rotational sensors with sufficient sensitivity to measure small rotations caused by earthquakes. Recently, however, rotations from teleseismic and small local earthquakes were successfully recorded (ring laser gyros, fiber optic gyros, electro-chemical sensors, etc.), in Japan, Poland, Germany, New Zealand, and Taiwan. This paper introduces the recently formed International Working Group on Rotational Seismology (IWGoRS) and its activities (http://www.rotational-seismology.org). This group aims to promote investigations of rotational motions (of ground and in structures) and their implications, and to facilitate sharing of experience, data, software and results in an open web-based environment. Its activities include publications, organizing professional meetings, and interactions with professional bodies in engineering and science. Anyone who is interested can join IWGoRS, and its website is freely accessible. H. Igel and W.H.K. Lee serve as co-organizers, and M.D. Trifunac leads the task force for strong motion and earthquake engineering. The IWGoRS recently organized the First International This meeting was attended by more than 60 participants from 13 countries. The key issues and research directions were reviewed with emphasis on their relevance for earthquake engineering. A special issue of the Bulletin of Seismological Society of America on Rotational Seismology and Engineering Applications is being prepared under the guest editorship of W.H.K. Lee, M. Celebi, M.I. Todorovska, and H. Igel, and is scheduled to appear in May, 2009. It will be dedicated to the emerging field of seismological research on all aspects of rotational ground motions (including theory, instrumentation, observation, and interpretation) from teleseismic and local earthquakes, as well as to rotations in structural response. It will contain original articles, short technical notes, in-depth and up-to-date reviews, and tutorials.

Reviews of Geophysics, 1983

In the last four years, there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study. New data from many local and regional networks of seismographs established during the previous four-year period, plus the now routine application of improved hypocentral location procedures, long-period body wave modelling, and moment-tensor inversion using digitally recorded data, have increased resolution of both the hypocentral location and the nature of the faulting process. Consequently, research emphasis has been on local tectonics, or those aspects of regional and global tectonics requiring high resolution. I briefly describe below some of the highlights of these studies. Shallow-Dipping Subduct ion A controversy over the dip of the subducting slab beneath central Peru and central Chile was resolved using data from local networks. Barazangi and Isacks (1976;1979) proposed, on the basis of a group of teleseismically determined hypocenters selected carefully for their quality, that the slab dips at an angle of only about 10 ø in these regions before dipping steeply several hundred kilometers inland. James (1978) questioned their event selection, pointing out that their model was based primarily on the seismicity from one local cluster of events. He preferred the model of Snoke et al. (1977;1979) of a slab dipping at about 30 ø , which was based on ScSp conversions within the dipping slab beneath western Peru. Data from local seismic networks (Hasegawa and Sacks, 1981; Suarez et al., 1982) revealed that the slab dips initially at an angle of about 30 ø beneath the coastal region of Peru, but then flattens out &md is nearly horizontal for several hundred kilometers. The cause of the unusually shallow subduction is not clear, but it may be related to the subductio• of a buoyant, aseismic, Nazca Ridge (Pilger, 1981). Plate Rheo logy The maximum depth of earthquakes in both oceanic and continental regions seems to be related to the tectonic age or surface heat flow of the province. Hence, the occurrence of seismic deformation is probably controlled by the temperature of the source region. Careful compilations of reliable focal depths in oceanic lithosphere show that the maximum depth age of the seafloor, with seismicity apparently confined above the 600 to 800øC isotherms (Chen and Molnar, 1982; Wiens and Stein, 1982).

During the Chilean earthquakes of May, 1960, a number of tall, slender structures survived the ground shaking whereas more stable appearing structures were severely damaged. An analysis is made of the rocking motion of structures of inverted pendulum type. It is shown that there is a scale effect which makes tall slender structures more stable against overturning than might have been expected, and, therefore, the survival of such structures during earthquakes is not surprising.

The basic problem of geophysics in more precise prognosing earthquakes and volcanoes’ eruptions has for decades been the erroneous idea of the very self matter and properties of the basic force of our Universe – the gravity force. This incorrect concept and errors in description of the Earth’s interior resulting from it cause that the astronomers see the motion of the planets as the motion in freefall. The universality of free fall (UFF) asserts that a point test body, shielded from all known interactions except gravity, has an acceleration that depends only on its location [1]. Point test body is an intellectual auxiliary object in physical theories and does not exist in the real universe. The whole momentum (impulse) of a real existing heterogeneous celestial body needs to be calculated by integration of momentum of all its material points dm=dV · ρ; dV - volume element, ρ- density . Therefore the whole momentum 'p' of a celestial body is vector sum of all momenta of all its parts of different densities: p = dm1· v + dm2 · v + . . . dmn· v = dV1 · ρ1 · v + dV2 · ρ2 · v + . . . dVn · ρn · v; p – momentum, v – velocity’ vector Hence the direct conclusion that each change of velocity or motion’s direction of a heterogeneous space object creates stresses in its interior between zones of different density, caused by inertia. It means that transformation of coordinate system to such where orbital centrifugal force does not exist is mathematically prohibited. Through this transformation the whole information concerning the internal structure of the celestial body and stress in its interior is lost. Therefore both the Free Fall and the Universality of Free Fall are myths that need to be rejected by physics as they block further development of geophysics and astronomy. After rejecting these myths we have to simply state that in the real existing universe the centripetal force always acts together with the centrifugal force. According to the action-reaction basis, none of these forces acts separately. Every real existing object of our universe becomes a centrifuge when rotating. No transformation of coordinate system can change this fact. It means that the signals registered at the University of Washington with the Eot Wash torsion balance apparatus have nothing to do with the Equivalence Principle or other problems of cosmology. These signals show only differences of orbital centrifugal force for test bodies of different density. Analysing these signals in terms of cosmological problems is a waste of time for physics.

Pure and Applied Geophysics, 2004

A wide set of dynamics phenomena (i.e., Geodynamics, Post Glacial Rebound, seismicity and volcanic activity) can produce time gravity changes, which spectrum varies from short (1… 10 s) to long (more than 1 year) periods. The amplitude of the gravity variations is generally in the order of 10 À8 …10 À9 g, consequently their detection requires instruments with high sensitivity and stability: then, high quality experimental data. Spring and superconducting gravimeters are intensively used with this target and they are frequently jointed with tiltmeters recording stations in order to measure the elastogravitational perturbation of the Earth. The far-field effects produced by large earthquakes on records collected by spring gravimeters and tiltmeters are investigated here. Gravity and tilt records were analyzed on time windows spanning the occurrence of large worldwide earthquakes; the gravity records have been collected on two stations approximately 600 km distant. The background noise level at the stations was characterized, in each season, in order to detect a possible seasonal dependence and the presence of spectral components which could hide or mask other geophysical signals, such as, for instance, the highest mode of the Seismic Free Oscillation (SFO) of the Earth. Some spectral components