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Seismology
Seismology
is a science branch that examine the occurrence and the
generation of earthquakes. In the following pages some information are
provided in order to explain how earthquakes are generated and
triggered, what is the known seismicity of some world areas, what is
the status on researching earthquake precursors signals and some web
pages with real time data are provided.
What is an earthquake
How earthquake are measured
How hearthquakes are recorded
Seismic precursor research
Electromagnetic
Emissions at Very Low Frequency
Chemical precusors
Earthquake Sequence analysis and Statistics
Chemical precusors
Earthquake Sequence analysis and Statistics
Important notice
This
page has the purpose to provide information to understand what it's an
earthquake, how it originates and how it can be measured.
Good
understanding of the concepts here contained it is important for the
comprehension of the information in this web site. The reader is
invited to examine these paragraphs and ask information and submit
questions by email or in the forum before proceed with the reading.
What is an earthquake
An
earthquake is,
in simple words, an energy release, accumulated in long periods of
time, from the underground structures. Meanwhile our planet
was
cooling during past geological eras, the earth crust faulting in
complex structures we call today "tectonica plates". These plates still
floating over fluid rocks below the earth's crust. This condition seems
to originates convective forces in slow motions. Slow motions but very
powerful. This effect would submit to great pressures and temperatures
many kinds of rocks that become elastic. The strain on these elastic
rocks accumulates in time like a giants "crossbow effect" while
enourmous rock extensions bends under unbelievable forces. When one of
these structures breaks, all the energy accumulated in years (sometimes
thousands of years) is released causing great vibrations that produce
different consequences depending on many factors. The type of the
fault, its orientation, deep, position from inhabitated places can
cause small effects or great devastations. Faults often spreads for
hundreds of kilometers. The geographic point on the surface where an
earthquake occurs is called EPICENTER. The exact location under the
surface (perpendicular to the epicenter) is called HYPOCENTER.
Tectonic
The earthquakes are almost totally caused by great volumes of ground movements from forces only partially known. Many theories are accepted. The one much widely accepted is the one that explain the earth surface is composed from many plates always in motions between each other. The borders of these plates touch each other and this produce a "noise". This noise is the "seismicity". You cannot listen this noise because it is subsonic. And much often these noise is released in "steps" in long term cycles during weeks, months, years, decades and millenniums...
The following picture illustrates how three portions of earth's crust can be in contact in different ways, but they are not the only observed in lands.
The earthquakes are almost totally caused by great volumes of ground movements from forces only partially known. Many theories are accepted. The one much widely accepted is the one that explain the earth surface is composed from many plates always in motions between each other. The borders of these plates touch each other and this produce a "noise". This noise is the "seismicity". You cannot listen this noise because it is subsonic. And much often these noise is released in "steps" in long term cycles during weeks, months, years, decades and millenniums...
The following picture illustrates how three portions of earth's crust can be in contact in different ways, but they are not the only observed in lands.
Plates movements
Hypotetical
convective movements, generated from the difference of
temperature in the fluid rocks belove the mantel would generate
movements on the material floating on it. Where convective motions
would have divergent directions a ridge is generated when they have
convergent motions a subduction boundary is generated.
The "tectonic" is a geology branch that study the processes of the crust deformation. The word come from Latin "tectonicum" from greek "tektonikos" that means "what concern the building".
The tectonic analyze the way of the actual shape of the earth's surface originates, in others words, how it is originated or built-up from the natural forces.
The "tectonic" is a geology branch that study the processes of the crust deformation. The word come from Latin "tectonicum" from greek "tektonikos" that means "what concern the building".
The tectonic analyze the way of the actual shape of the earth's surface originates, in others words, how it is originated or built-up from the natural forces.
Movements of the ground
Some kind of earthquakes (tipically with small energy release) are generated by underground landslides or huge rock or ground block falling from cave ceiling.
Usually this kind of earthquakes even if recorded by near deployed instruments, don't generates effects on buildings, unless the underground landslide doesn't generates direct effect on the surface with a chasm.
While we have not a deep knowledge of the engine that moves the continental plates to moves and friction each other, the movement produced near the surface are better known. In the points where two continental plates have friction they generates faults of many types. The faults become complex fault systems with a complex behaviour.
Some kind of earthquakes (tipically with small energy release) are generated by underground landslides or huge rock or ground block falling from cave ceiling.
Usually this kind of earthquakes even if recorded by near deployed instruments, don't generates effects on buildings, unless the underground landslide doesn't generates direct effect on the surface with a chasm.
While we have not a deep knowledge of the engine that moves the continental plates to moves and friction each other, the movement produced near the surface are better known. In the points where two continental plates have friction they generates faults of many types. The faults become complex fault systems with a complex behaviour.
The following picture illustrates how could be a fault system structure.
Keep
in consideration that each block is always subjected to the
gravity force making it "to fall" on the structures below. The gravity
force is balanced by the lateral forces coming from various directions
that can keep-up an entire area or ground block.
Looking at the fault system we can find at least four type of faults. Each one is capable to generates different earthquakes with force and movements that produce different effects on the surface. You have also to consider that the four specific fault listed below are never ONLY of that kind, they are usually part of a system of faults and have azimuth and orientation that make a fault a mix of some kind of faults. For istance a fault basicly called "direct or normal" can have also a "lateral" motion as in the "lateral slip fault" or vice-versa. So, the movement listed below, are to be considered "basic movements"
Looking at the fault system we can find at least four type of faults. Each one is capable to generates different earthquakes with force and movements that produce different effects on the surface. You have also to consider that the four specific fault listed below are never ONLY of that kind, they are usually part of a system of faults and have azimuth and orientation that make a fault a mix of some kind of faults. For istance a fault basicly called "direct or normal" can have also a "lateral" motion as in the "lateral slip fault" or vice-versa. So, the movement listed below, are to be considered "basic movements"
Direct fault or
normal fault
The direct fault or also called normal fault is so called becaus the vertical motion of the fault is usually caused by the gravity force. The two blocks subjected to divergent forces, they extent each other leaving space to make the block that remains more free to fall down and it slides where there it find space.
The direct fault or also called normal fault is so called becaus the vertical motion of the fault is usually caused by the gravity force. The two blocks subjected to divergent forces, they extent each other leaving space to make the block that remains more free to fall down and it slides where there it find space.
Reverse fault
The reverse fault is subjected to compressive forces (the opposite of the inverse fault).
The two blocks slide each on the other and they moves up or down each other depending on the fault orientation.
The reverse fault is subjected to compressive forces (the opposite of the inverse fault).
The two blocks slide each on the other and they moves up or down each other depending on the fault orientation.
Thrust Fault
This kind of fault is originated tipically by compressive forces and it can be also called a inverse fault. But the fault plane have a modest inclination and this cause the overlap of one side of the fault over the other side of ground.
This kind of fault is originated tipically by compressive forces and it can be also called a inverse fault. But the fault plane have a modest inclination and this cause the overlap of one side of the fault over the other side of ground.
Strike slip fault
This kind of fault generates and it is moved by horizontal motions, the two sides of ground slide each other in a horizontal movements.
This kind of fault generates and it is moved by horizontal motions, the two sides of ground slide each other in a horizontal movements.
Damages from
earthquakes
Every ground vibration can potentially cause damages to structures. Seismic waves that usually produce more damages than all others are the horizontal waves, this is true especially for buildings not built to resist to earthquake shakes. The following pictures shows some damages on buildings after earthquakes.
Every ground vibration can potentially cause damages to structures. Seismic waves that usually produce more damages than all others are the horizontal waves, this is true especially for buildings not built to resist to earthquake shakes. The following pictures shows some damages on buildings after earthquakes.
How earthquakes
are measured
Earthquakes are detected by seismometers and then recorded by seismographs. Analyzing the seismogram and knowing the mechanical and electric responseof the seismometer and the system that pick its signal seismologists can recovery the exact motion of the ground.
Earthquakes are detected by seismometers and then recorded by seismographs. Analyzing the seismogram and knowing the mechanical and electric responseof the seismometer and the system that pick its signal seismologists can recovery the exact motion of the ground.
Earthquakes
are measured using basicly two international measurement
scales the Mercalli and the Richter scales. The Mercalli scale give an
extimation of the earthquake intensity based on the extimation of the
physical effect of the shake (often called macroseism effects) over
people, things, buildings and environement. The Richter scale has the
purpose of measure the magnitude or the total energy released by the
earthquake. The two scales can easily NOT correspond because the
damages of a powerful earthquke happened very deep undregrounf cause
minimal effect on surface and viceversa a small earthquake very shallow
can cause heavy damages to building near the epicenter.
Anyway keep present that speaking about magnitude it is always referred to the energy released by a quake and speaking about intensity is referred to the Mercalli scales with its description of the effect over the people.
Anyway keep present that speaking about magnitude it is always referred to the energy released by a quake and speaking about intensity is referred to the Mercalli scales with its description of the effect over the people.
- 1st - Imperceptible
Microseismic shake detected only by instruments near to the earthquake epicenter. - 2nd
- Very light
Microseismic shake detected by instruments at certain distance from epicenter. - 3rd
- Light shake
Population feel the shake but only at high floors of tall buildings, it can be confused with a passage of an heavy truck. - 4th
- Moderate shake
Felt by people inside building rarely on free field - 5th
- Intermediate shake
Felt almost by all population even at ground floor, some sleeping people are awaken, chandeliers oscillates and small objects moves on shelves. - 6th
- Strong shake
Everybody feel this kind of shake that cause movements of furnitures and object drops, churches bells can beat sound due to the strong oscillations. - 7th
- Very strong shake
Beds are oscillating, walls can be damaged even in robus houses, tails are moved over the ceiling and roof ridges can fall, people have difficult to keep standing. - 8th
-Extremely strong shake
Heavy furnitures and shelves can fall, veichles are disturbed while travelling, heavy damages on buildings and foundations can be damaged. - 9th
- Distructive shake
People are in panic, damage to buildings usually capable to resist to earthquakes, other buildings collapse and water in lakes shake too. - 10th
- Very distructive shake
Destruction of many buildings also the more robust ones, landslides and railroads are damaged, tsunamis happens in coasts - 11th
- Total destruction
Total distruction of buildings, large faults opens in the ground, collapse of dams and bridges. - 12th
- Catastrofic
Total distruction of all building and facilities, persons and objects can be launched on air, landscapes are modified with modifications on lakes, rivers and hills.
In 1953 the
seismologist Charles Richter defined the magnitude of
an earthquake as the:base 10 logarythm of maximum amplitude recorded in
micron obtained with a standard seismograph placed at 100km from the
epicenter. Of course other parameter allow to adjust the
scale to
the variables distances from epicenters. Furthermore other types of
magnitude has been defined such the local magnitude , surface magnitude, duration
magntude and so on....
Tables based on observation of the local crustal physical morphology are also available to scientific observatories. The measurement and the corresponding comparison tables can also vary using different types of sensors. Here is reported the standard equation for the magnitude computation valid basicly only for the California area where Charles Richter made his experiments.
Tables based on observation of the local crustal physical morphology are also available to scientific observatories. The measurement and the corresponding comparison tables can also vary using different types of sensors. Here is reported the standard equation for the magnitude computation valid basicly only for the California area where Charles Richter made his experiments.
ML
= log (micron of peak amplitude) + 3 x log(km distance from epicenter)
– 3.37
TheRrichter's scale can be compared to the power released of various type of bombs
- M 0 - 2 < 2 x 10^10 Erg (0.5 Kg of TNT)
- M 2 - 3 < 3000 x 10^10 Erg (50 tons of TNT)
- M 3 - 4 < 3.5x10^15 Erg
- M 4 - 5 < 15x10^16 Erg (Small atomic bomb of 20 kiloTons)
- M 5 - 6 < 150x10^18 Erg
- M 6 - 7 < 120x10^20 Erg (Small Hydrogen bomb of 1 megaTons)
- M 7 - 8 < 30x10^22 Erg (100 Hydrogen bombs)
- M 8 - 9 > 1 x 10^25 Erg (60,000 Hydrogen bombs)
The Seismometer
A seismometer is an instrument, a sensor, capable to detect vibration produced by a seismic motion.
Vibration are of course detectable near the epicenter but they also travel at great distance proportionally to the earthquake magnitude. Seismometers are usually capable to detect VERY small vibrations also at great distances. A sensor (a seismometer) transform (transduce) the mechanical motion in an electric signal. To detect earthquake usually seismometer use the intertial principle that a mass "suspended" over a spring or in other way disengaged from the ground motion will remains almost steady in respectof the ground. Then appropriate transducer will detect the relative motion between the mass and the ground. Depending of the type of suspension and the transducer used the signal can represent: relative velocity, acceleration or rarely position.
Of course from each of these three measurement units is possible to retrieve the other two. All measurements are subjected of quantization errors (measurement errors) the seismologist need to know this error and compensate the reading for it (if possible). A professional seismometer must be capable to detect signal in the order of nanometers or fraction of them. For an amateur seismologist is not a problem makeup a seismometer capable to resolve signal down to10-50 nanometers that is a good result indeed for a homebrew project. Such seismometer will be capable to detect almost all microseismic in a radius of 50km from the detecting point, the majority of earthquakes with magnitude over 5.0 in a radius of 1000km and virtually all earthquakes with magnitude over 7.0 from all over the world. I say virtually because an intrinsic limitation of detecting earthquake from all the planet is given by the shadow zones. Each seismic station has a band of globe that happear "in shadow" from the main waveforms of a seismogram.
A seismometer is an instrument, a sensor, capable to detect vibration produced by a seismic motion.
Vibration are of course detectable near the epicenter but they also travel at great distance proportionally to the earthquake magnitude. Seismometers are usually capable to detect VERY small vibrations also at great distances. A sensor (a seismometer) transform (transduce) the mechanical motion in an electric signal. To detect earthquake usually seismometer use the intertial principle that a mass "suspended" over a spring or in other way disengaged from the ground motion will remains almost steady in respectof the ground. Then appropriate transducer will detect the relative motion between the mass and the ground. Depending of the type of suspension and the transducer used the signal can represent: relative velocity, acceleration or rarely position.
Of course from each of these three measurement units is possible to retrieve the other two. All measurements are subjected of quantization errors (measurement errors) the seismologist need to know this error and compensate the reading for it (if possible). A professional seismometer must be capable to detect signal in the order of nanometers or fraction of them. For an amateur seismologist is not a problem makeup a seismometer capable to resolve signal down to10-50 nanometers that is a good result indeed for a homebrew project. Such seismometer will be capable to detect almost all microseismic in a radius of 50km from the detecting point, the majority of earthquakes with magnitude over 5.0 in a radius of 1000km and virtually all earthquakes with magnitude over 7.0 from all over the world. I say virtually because an intrinsic limitation of detecting earthquake from all the planet is given by the shadow zones. Each seismic station has a band of globe that happear "in shadow" from the main waveforms of a seismogram.
How earthquake are
recorded
Recording of seismogram was obtained in past using rotating drums where a pen was writing by thermal transfer using thermal paper, for sometime also magnetid tapes has been used.. At moment the majority of observatory use a digital electronic recording methods and the seismograophs are recorded in digital media such hard disks, CD, DVD etcetera.
This way to record the signal digitally not only improve the dynamic range of the signal but also allow the scientists to make a number of extra measurement and computation over the signal. Heavy numerical analysis can be applied such spectrogram and several type of filtering can be applied to retrieve all needed information from the digital master track.
To have the possibility to analyze the signal in digitial the electric continous signal have to be converted from the "analogic" form to the "digitial" forms.
Together with thesignal containing the information about the ground motion are also recorded the geographic coordinates of the detecting place and the absolute time usually expressed in UTC (Universal Time Coordinated) or known as well as the Greenwich Mean Time GMT.
Data about the calibration of the sensor and the system to it connected are also needed for professional seismologists and evoluted amateur seismologists.
Recording of seismogram was obtained in past using rotating drums where a pen was writing by thermal transfer using thermal paper, for sometime also magnetid tapes has been used.. At moment the majority of observatory use a digital electronic recording methods and the seismograophs are recorded in digital media such hard disks, CD, DVD etcetera.
This way to record the signal digitally not only improve the dynamic range of the signal but also allow the scientists to make a number of extra measurement and computation over the signal. Heavy numerical analysis can be applied such spectrogram and several type of filtering can be applied to retrieve all needed information from the digital master track.
To have the possibility to analyze the signal in digitial the electric continous signal have to be converted from the "analogic" form to the "digitial" forms.
Together with thesignal containing the information about the ground motion are also recorded the geographic coordinates of the detecting place and the absolute time usually expressed in UTC (Universal Time Coordinated) or known as well as the Greenwich Mean Time GMT.
Data about the calibration of the sensor and the system to it connected are also needed for professional seismologists and evoluted amateur seismologists.
A seismogram recorded on paper has this appereance:
A seismogram recorded digitally show as this one:
(double click on it for a complete view)
First
seismographs
First seismographs had very poor performance and they was capable to track only strong motions. Anyway they was capable to give a good measurement of the peak impulse. The following picture show one of the oldest but effective seismograph capable to track on sand the ground motion. It was a simple pendulum kept disengaged from the ground by a long coard hanged on the high ceiling of an olde medieval building. It has been built in 1751 from the monach Andrea Bina and it is still working (for educational purposes) in Perugia, Italy in the local seismic observatory that is titled to his founder Andrea Bina himself.
Other seismographs was using as writing paper a smoked paper, then a pencil was scraping the smoke leaving a white track. Such type of seismograph had to overcome the pen friction on the paper so very heavy mass were used with a complex lever systems. Also these seismographs can be see at operation in the Andrea Bina observatory that has 3 of these old fashion seismographs.
First seismographs had very poor performance and they was capable to track only strong motions. Anyway they was capable to give a good measurement of the peak impulse. The following picture show one of the oldest but effective seismograph capable to track on sand the ground motion. It was a simple pendulum kept disengaged from the ground by a long coard hanged on the high ceiling of an olde medieval building. It has been built in 1751 from the monach Andrea Bina and it is still working (for educational purposes) in Perugia, Italy in the local seismic observatory that is titled to his founder Andrea Bina himself.
Other seismographs was using as writing paper a smoked paper, then a pencil was scraping the smoke leaving a white track. Such type of seismograph had to overcome the pen friction on the paper so very heavy mass were used with a complex lever systems. Also these seismographs can be see at operation in the Andrea Bina observatory that has 3 of these old fashion seismographs.
Modern
Seismographs
Recent technology allow scientist to have very small seismometer, sometime with mass weight of grams or at maximum few hundreds of grams. In fact it is is not the mass to determine the sensitivity of the seismometer but the transducer applied to it and the quality of the electronic circuits connected to it. The signal is then converted to digital and transferred to a computer.
At moment almost all observatories are using desktop computer to record seismographs. Data can be after analyzed by scientist of all the world sharing the data on internet or in other suitable media.
The following picture show a personal computer equipped for earthquake recording.
A digitial seismogram allow the user to apply a number of observation on it. Proper filtering algorythm are capable to retrieve the signal also from a "dirty" seismograph. Of course the original master tracks are always left unaltered as base for futher different analysis.
Furthermore the digital recording allow a single person to analyze quickly tents of seismograms and have the ability to determine the epicenter and the hypocenter.
Modern real time analysis tecniques allow to have almost a real time determination of an earthquake allowing to examine the focal mechanism of the earthquake (that give information on the type of motion generated by the shake) allowing to determine the magnitude and the potential effect on the stroke area. This of course have good impact on the search and rescue teams that can be alerted and sent to the place in a shorter time.
Precise event localization can give experts the ability to determine how an earthquake can influcence the nearby faults and if it can be capable to trigger other earthquakes in different areas.
Recent technology allow scientist to have very small seismometer, sometime with mass weight of grams or at maximum few hundreds of grams. In fact it is is not the mass to determine the sensitivity of the seismometer but the transducer applied to it and the quality of the electronic circuits connected to it. The signal is then converted to digital and transferred to a computer.
At moment almost all observatories are using desktop computer to record seismographs. Data can be after analyzed by scientist of all the world sharing the data on internet or in other suitable media.
The following picture show a personal computer equipped for earthquake recording.
A digitial seismogram allow the user to apply a number of observation on it. Proper filtering algorythm are capable to retrieve the signal also from a "dirty" seismograph. Of course the original master tracks are always left unaltered as base for futher different analysis.
Furthermore the digital recording allow a single person to analyze quickly tents of seismograms and have the ability to determine the epicenter and the hypocenter.
Modern real time analysis tecniques allow to have almost a real time determination of an earthquake allowing to examine the focal mechanism of the earthquake (that give information on the type of motion generated by the shake) allowing to determine the magnitude and the potential effect on the stroke area. This of course have good impact on the search and rescue teams that can be alerted and sent to the place in a shorter time.
Precise event localization can give experts the ability to determine how an earthquake can influcence the nearby faults and if it can be capable to trigger other earthquakes in different areas.
Seismic precursors research
Introduction
These
page are provided with the intent of inform people and discuss with
experts on what has been done until now in the research of precursors
signals. Phonoseismology is relaated to the playback acceleration of
digital seismic data up to reach the audibile range of the human ear.
This process is called also seismic data audification. The radio
reception of Very Low Frequency electromagnetic emissions is another
field to be better explorated. Chemical precursors in soil, water and
near surface atmosphere are well known as seismic precursors,
unfortunately not a reliable pattern has been obtained to have a
reliable earthquake warning. Earthquake sequence statistical analysis
is a method that use a statistical computation to evaluate the
probability of an event of a certain magnitude can happen in a certain
area.
Phonoseismology a new approach to seismic analysis and the precursors signal research
Phonoseismology
is a new name coined by Mauro Mariotti and Andrea Cellini in April 1999
when they started to catalogue noises recorded by their seismic
station. The method proposes an organolectic description of the seismic
signal recorded by a seismometer or accelerometer. While we cannot yet
claim to have identified a specific pattern as a "seismic precursor" we
can state that there are strong indications presence of some
kinds of precursor signals.
The method
The
method is based on the high speed playback of seismic signals recorded
in digital media so that they become understandable by the human ear.
The seismic signals are about a few Hz (oscillation per second) and
cannot be heard until the frequency has been shifted to at least
30-50Hz. Some subsonic signals are perceived by animals like cats and
dogs. Very often animals become very agitated just before an
earthquake. We don't know at moment if animals are excited by
mechanical vibrations, by electromagnetic fluctuations, or by other
natural phenomena. The fact remains that the acoustic deficiency of the
human ear below certain frequency can be improved using this method of
seismic acceleration and allows the ear to detect the strange patterns
occurring just before and after a quake, with a retrospective analysis.
The artificial noise
Using this method you can examine the noise present in the ground over a vast area. This method could also be used to study the effect of subsonic noise generated by factory and highway, on human health.
In the following WAV file trucks are easily detectable, passing near to the seismic station on a busy road. From the signal duration and the site of the sensor we were able to determine that a truck can generate detectable noise in the ground at least 1.5 kilometres (around 1 mile) away. The acceleration of the signal is of 500 times. An experienced listener will be able to detect the subsonic doppler effect.
Download Piece of recorded signals without quakes, but are easily recognised, at 500 times the original speed. TRUCKS.ZIP
The artificial noise
Using this method you can examine the noise present in the ground over a vast area. This method could also be used to study the effect of subsonic noise generated by factory and highway, on human health.
In the following WAV file trucks are easily detectable, passing near to the seismic station on a busy road. From the signal duration and the site of the sensor we were able to determine that a truck can generate detectable noise in the ground at least 1.5 kilometres (around 1 mile) away. The acceleration of the signal is of 500 times. An experienced listener will be able to detect the subsonic doppler effect.
Download Piece of recorded signals without quakes, but are easily recognised, at 500 times the original speed. TRUCKS.ZIP
A local earthquake
The following file is a seismic event occurred on the 10 October 1999 of 4.8 Richter at around 100 km from the seismic station. There are no seismic precursor signals.
Download Rieti (Italy) event of 10th October 1999. RIETI.ZIP
A precursor like a condensator charge
This
precursor is called "as condenser charge" and in it is evidence a
frequency that appears on the low part of the frequency range of the
sensor increasing in a parabolic envelope. At the high side of the
parabola, touching the frequency of around 1Hz the quake happens.
The signal disappeared with the quake. It is very weak but it was easily recognised using a spectrum analyser. That quake was a 4.8 and it was located in Valfabbrica (Perugia, Italy). The signal was a precursor of around 2 hours.
The signal disappeared with the quake. It is very weak but it was easily recognised using a spectrum analyser. That quake was a 4.8 and it was located in Valfabbrica (Perugia, Italy). The signal was a precursor of around 2 hours.
Download Valfabbrica, Perugia, Italy earthquake of 22nd June 2000
On
this picture you can see the horizontal bright line that is related to
the natural period of the seismometer around 1 Hz. The yellow and red
track is the seismic event that spread signal on all frequencies. The
spectral analysis showed a weak signal which appeared just a while
after the beginning of the chart low left side. That signal increased
in frequency until it reached 1 Hz, when the quake occurred. We
don't know if it is one of the mechanical vibrations or electromagnetic
noise recognised by animals, but it seems VERY interesting.
An impulsive precursor
This precursor has been called 'impulsive' in the sense it is formed by single impulses before and after a quake. The signal is easily recognised, even if, due to the acceleration, it is very brief. Try to listen it many times you can identify it very well. The signal is a precursor of around 30 minutes
Download Badia Tebalda, Arezzo, Italy of 29th April 2001
This signal is of different kind maybe due to a different seismogenetic
nature. We find more frequencies related to the precursor. The sensor,
a different one, has a resonance frequency of 1.4 Hz (slightly higher
than the other shown before). The quake is on the yellow vertical band
on the right side of the chart. Just before this you can see 6 impulses
and after it another 2 or 3 impulses.
The rhythm of that impulses and their sound are very different from other impulses recorded and recognised as civil noise.
The rhythm of that impulses and their sound are very different from other impulses recorded and recognised as civil noise.
Potential precursors at very low frequencies for telesesimic warning
The presence of precursors signal even before and after a quake seems to be confirmed by a workgroup called ELFRAD specialised on ELF (Extreme Low Frequency) http://www.elfrad.com.
This is not too strange, since a quake may be only the climax event of a complex series of events and mechanisms unknown at the moment, which may endure for many months and years even before and after the main shock. The Elfrad Group, who have specialised in the analysis of electromagnetic anomalies, recognise that electromagnetic signals are detectable before and after a quake. One example of that is related to the signal recorded in occasion of the devastating earthquake of Taiwan on September 1999
Download Taiwan 20 September 1999
There are three files. TAIW1.WAV x 4000 times the original speed, TAIW2 x 8000 and TAIW3 x 16000 on that is easily detectable the possible precursors similar to a jet noise.
Download Turkey 10 Dicember 1999
The single WAV file is accelerated 8000 times. The quality of digital data is not high but it is still possible to recgnise a precursor signal.
The picture reported below is referred to the Taiwan quake of 20 September 1999.
It
represents the signal spectrum of the day 20th and 21st September 1999,
the black area indicates absence of signal on that frequency and the
blue and yellow areas indicates a signal of increasing intensity. The
green lines are drawn by hand to show the envelope of the precursor
signal. The tail after the quake seems not to be due to earth crust
resonances after the quake, but seems to be correlated to the quake
event itself. This chart shows in two dimensions the intensity of the
frequency in the range from 0.23 e 0.27 Hz recorded in the 46 hour
before the quake and the next 68 hours of the Tawian quake of Ms6.75
del 20 September 1999 17:47 UTC. The quake corresponds to the peak on
340 unit of the horizontal divisions.
In
the last period of time we have recorded a few other events that
activate signals like these. We don't know of an explanation for the
phenomena even if we know that similar signals are present during storm
fronts and barometric changes. But the strange thing is that we often
observe similar kinds of signals without barometric changes and also
the opposite case of no signals in presence of strong storms and low
atmospheric pressures fronts.
This could give support to the hypothesis of a relationship between the crust deformations and the frequency response alteration of the crust in geologically actives areas.
This could give support to the hypothesis of a relationship between the crust deformations and the frequency response alteration of the crust in geologically actives areas.
Conclusions
At
the moment we cannot state we have discovered a stable and
repeatable precursor. We are enthusiasts of this approach that has
given these good results. The "phonoseismology" could become a viable
analytical tool, especially if applied in wide range of sismogenetic
locations and with better equipment, designed expressly for it. In the
future automatic machines trained to detect specific precursors could
be used to extend seismic warning systems.
Other interesting sites
Earthquake forecast with Acoustic Emission
http://www.deci.com/poe.htm
Extreme Low Frequency research group
http://www.elfrad.com
RadioGeophonics by Adriano Nardi (GAIA Project)
http://space.tin.it/scienza/adnardi
Spectrogram by Richard Horne
http://www.monumental.com/rshorne/gram.html
Latest development
Recently
we found in the web some other researches accomplished by other
scientists about the so called "audification of seismic data". The term
is different from phonoseismology but regards exactly the same concept.
We didn't had the pleasure to read these paper before our study; anyway
making searches on the web with the keywords: "seismic" and
"audification" we found some other links that refers to experiences and
works made sice the year 1995. We are firmly convinced that
this could be a productive path to the research of reliable precursor
signal patterns. Probably not all earthquakes will release precursors
signal translable to the acoustic sound spectra but even if only a
little percentage of earthquakes could be monitored before they occurs
and identified giving a useful warning it would be always an advantage.
We are also convinced that the phonoseismological study of the seismic
genesis will complete the knowledge of active seismic zone and discover
unknow seismic zones.
Interesting Papers found over Internet
http://geology.heroy.smu.edu/~hayward/
http://www.techfak.uni-bielefeld.de/ags/ni/projects/datamining/datason/datason_e.html
http://computing.unn.ac.uk/staff/cgpv1/caitlin/Downloadables/Thesis/Chapter%202.pdf
http://www.acoustics.hut.fi/icad2001/proceedings/papers/dombois.pdf
http://www.icad.org/websiteV2.0/Conferences/ICAD97/Valenzuela.pdf
http://www.nada.kth.se/~fredrikw/lic/Licentiate_thesis.pdf
VLF - Very Low Frequency
VLF Very low frequency and ELF Extreme low frequency radio spectrum are field of research of earthquake precursors signals. People wanting to submit an article for this page are welcome.
Chemical and Physical precursor signals
Chemical and phisical changes in sources waters are also well known earthquake's precursors even if not well understood. Also changes in resistivity, conductivity and impedance of the ground are object of analysis. To do not forget the variation of geomagnetic fields.
People wanting to submit an article for this section are welcome.
Statistical analysis of earthquake sequence
Scientists
of the Swiss Seismological Service and the Advanced
National Seismic System (ANSS) have collaborated to develop
techniques that quantify the increased likelihood of future earthquake
shaking from earthquake clusters in California.
In this system, the probability of strong earthquake
shaking in the next 24 hours is calculated. The system
considers all the earthquakes, large and small, that are recorded by
some seismic networks. For each event, the probability that it will be
followed by an earthquake large enough to cause strong shaking is
calculated from the known behavior of aftershocks and the possible
shaking pattern predicted from historic patterns. A map is edited with
this information you can find an example of this map here.
In nature aftershocks occur at
a defined rate but the time of any one is random. Nobody can say when
the next aftershock will happen but it is possible
to determine a probability that an aftershock will occur
during a given interval of time. For example Just after a very big
earthquake, the probability of a strong aftershock is 80%. However,
after a M3 event, there is only a probability of 0.0002%.
Even though this is very low, it is higher than it would be if the M3
had not occurred.
This computation is also combined with the "background probability" of
shaking based on data of the National Hazard Maps (USA). This
background probability does not change with time. The highest
probabilities in California are near San Francisco and Los Angeles and
reach 1 in 10,000 per day. The system then considers all the
earthquakes, large and small, that are recorded by the California
Integrated Seismic Network (CISN). For each event, the probability that
it will be followed by an earthquake large enough to cause strong
shaking is calculated from the known behavior of aftershocks. The
shaking that would be produced by such an earthquake is then predicted
from the known relations between earthquake size and shaking patterns.
The likelihood of that shaking is then added to the background
probability on the map.
Note of Mauro Mariotti
It would important for people to understand that probability of an earthquake should not modify the life habits and customs; it would modify the building methods and lead people to put in practices simple rules to protect themselfs from earthquakes (for example fixing the shelves on the wall to avoid their falling, or avoid to put heavy objects near or over the bed, especially over kids beds). Earthquake forecast would be something to consider like the probability to have rain instead of blue sky. It would never be considered "earhquake predictions" but only "forecasts". Even though the weather forecast are very developed and well accepted by population (eitther in their good forecasts and also with the bad ones) the same would be needed for earthquake forecast. Population educated to know the earhquake hazard and risk woud be more mature for a future when earthquake could be forecasted more precisely.
It would important for people to understand that probability of an earthquake should not modify the life habits and customs; it would modify the building methods and lead people to put in practices simple rules to protect themselfs from earthquakes (for example fixing the shelves on the wall to avoid their falling, or avoid to put heavy objects near or over the bed, especially over kids beds). Earthquake forecast would be something to consider like the probability to have rain instead of blue sky. It would never be considered "earhquake predictions" but only "forecasts". Even though the weather forecast are very developed and well accepted by population (eitther in their good forecasts and also with the bad ones) the same would be needed for earthquake forecast. Population educated to know the earhquake hazard and risk woud be more mature for a future when earthquake could be forecasted more precisely.