As we all know, Earthquakes are the most destructive among all the natural hazards. Most of the time, they occur without any warning, which makes them most feared and unpredictable natural phenomena. Globally, on average, two earthquakes of magnitude 8 are known to occur every year. Iran is surrounded by tectonically active zones. Earthquakes are regularly felt on all sides of Iran. But the capital, Tehran, has been fortunate enough to avoid a major quake this century. Tehran was shaken in 1830 by a magnitude 7.2 quake. A recent earthquake in the northern part of Iran has raised the stakes for people who are interested to know whether or not earthquakes can be predicted. Recently, like many others, I received a message saying that Dr. Rahmi Tabar has predicted an earthquake in Tehran within the next 10 days (now 6 days).
What was interesting was not necessarily the validity or credibility of such a prediction, but the way even educated people, like those in the Sharif University of Technology narrated the messages.
A comprehensive look at the literature shows little success in predicting earthquakes. The first successful prediction of a major earthquake was made in 1975. The earthquake took place in China (Haichung) on Feb. 4, 1975. The intensity of the earthquake was 7.3 on the Richter scale, and about ninety percent of the structure was destroyed in a city of 90,000 people. In this case thousands of people were saved by the massive evacuation from unsafe housings just before the earthquake. The short-term prediction was possible primarily on a series of foreshocks that began four days prior to the main shock. Unfortunately these types of short-range prediction on the basis of foreshock are not always reliable. Earthquake prediction by any geoscientist is far from success, however a detailed and systematic investigation may lift haze in its prediction. Earthquake prediction in an area may be carried out under the following heads:
a. Lithological characterization and structural setting of the region
b. Crustal deformational studies
c. Frequency of foreshock
d. Repetitive land level survey
e. Water tube tiltmeters
f. Geomagnetic observation
g. Geothermal gradient
h. Gravity survey
i. Hazard mapping
Lithological Characterization and Structural Setting of the Region
Geological mapping of an area is the first step towards the surface and subsurface investigation of a region. The accuracy of these investigations decides the prediction accuracy before an earthquake and also the post earthquake control and reduction measures. The advent of Geoinformatics has brought revolutionary change in these investigations. Nowadays, a number of geological software packages are available in the market for the geological mapping of an area. These software packages are highly useful in the speedy and accurate execution of mapping work. The arrival of GPS has the capability of recording spatial co-ordinates with an accuracy level of up to a millimeter. Remote sensing and air photogrammetry is of immense potential at the reconnaissance stage of the mapping. Now, it is possible to map the inaccessible regions through the satellites. Structural setting indicates the future earthquake by giving enough information regarding the palaeoseismology of the area. It is also helpful in the hazard mapping of the area to take preventive and control measures. Carrying out systematic lithological mapping of the terrain can very well minimize the magnitude of seismic destruction. It has been observed that the structures on a consolidated foundation, e.g. igneous and metamorphic rocks, are safer than those on unconsolidated basements, viz. Alluvial, sand and loamy soil. Different surface materials behave differentially in response to seismic shaking of various frequencies. Unconsolidated earth materials (mud, alluvium, and bedrock) vibrate more compared with hard bedrock. Therefore, an area sensitive to earthquake hazards must be mapped for it to be available to land-use decision makers. So a highly accurate geological map can be prepared with the help of recent geomatic tools and they can be analysed through GIS to use it for the prediction, or the preparation of action plan during the post earthquake rehabilitation measures. By predicting the intensity of shaking due to an earthquake before the earthquake occurs, we can help plan to prevent damage. Doing this rapidly after an earthquake can help manage the emergency response efforts. Intensity is a measure of the effects of earthquakes. Examples include damage to man-made structures, ground failure and felt shaking. Intensity is not the same as magnitude, although it is influenced by earthquake magnitude. Intensity is also influenced by distance from the fault, ground conditions, and sometimes, directivity. The most commonly used intensity scale today is the Modified Mercalli Scale. This is the scale we have used in the predictive models. These predictive intensity maps have been generated following the method described in the 1995 ABAG report "On Shaky Ground" by Jeanne Perkins and John Boatwright
Crustal Deformation Studies through GPS
Throughout the world, most of the earthquake activities are confined to plate margin associated with crustal deformation. Nowadays, crustal movement can be recorded with high degree precision using GPS. Crustal deformation through GPS is one of the fast emerging areas, and most probably, the only area where the real potential of GPS lies as far as effective earthquake predictions are concerned. GPS is now being used effectively for monitoring of crustal movement. In modern time, earthquakes are studied with more authenticity, as high quality seismic and geodetic data are available globally. Progress in this field with the establishment of broad-band digital seismograph and geodetic network. Data accumulated through the seismological, geological and geodetic observations can be of great help in the delineation of the earthquake-prone areas. This will have direct impact on the hazard assessment and public safety measures.
Frequency of Foreshock
There are cases where minor foreshocks have indicated the major coming shock. So, it is highly desirable to establish a seismological observatory for the continuous monitoring of seismic activity in an area. In modern time, earthquakes are studied with more authenticity, as high quality seismic and geodetic data are available globally. Data accumulated through the seismological, geological and geodetic observations can be of great help in the delineation of the earthquakes prone areas. This will have direct impact on the hazard assessment and public safety measures. On that basis countries can be divided into 5 zones with respect to intensity of earthquake. Of these, zone V is seismically the most active where earthquake of magnitude 8 or more could occur. Zone I is the least active region. There are various parameters, which can be analyzed collectively for the purpose of an earthquake prediction. Surface parameter include topographical changes and subsurface parameter includes subsurface geomagnetic, geothermal and gravity variation. Rates of uplift and subsidence, especially rapid or anomalous change may be significant in predicting earthquakes. For example, for more than ten years before the 1964 earthquake near Nigata, Japan, there was an anomalous uplift of the earth crust. It has also been observed that the speed of primary waves may decrease for a month, and then increase to normal just before an earthquake. With recent advancement in science and technology, a proper sensor developed to measure these variations can be put on satellite to get regional idea by periodic and continuous monitoring of these variations and their quantification may helps us in forecasting such hazardous events. Changes in the electrical resistance of an area have also been reported before earthquakes. Increase in the amount of radioactive radon gas that is dissolved in deep well water has also been reported.
Dr. Rahimi Tabar's Study and Its Impact on Society
Dr. Rahimi Tabar's study as published in the LANL pre-print archive (arXiv) is definitely an admirable effort at linking changes in surface resistivity of the granites to Earthquakes. This is an interesting proposed correlation, although the paper in the archive was not at all well-written, and would have qualified more for a detective magazine than an academic publication, but I can understand that they wanted their paper to be out there so their idea would be preserved. Perhaps that correlation can be used for linking the two phenomena, perhaps it can't; time will show, but one observational experiment in itself would not be sufficient to predict an Earthquake in Tehran with a resolution of 10 days, let alone determine whether the order of magnitude would be directly correlational with the extent of changes in resistivity (the earthquakes measured in the study for Yazd were 3.1 Richters or less).
Generally, publishing something this rudimentary even in the arXiv is not good practice, although other people do this too. What really upsets me (and I have had discussions on this with students in Iran who were willing to swear by Dr. Rahimi Tabar's results) is the way a very rudimentary, and at this point raw finding, which would not qualify for a conference proceeding, let alone an academic journal is used as "scientific" evidence that earthquakes can be predicted within a 10 day period (the messages didn't have probabilities, order of magnitudes, or anything like that). Whether Sharif University and Dr. Rahimi-Tabar are willing to do this is their issue, but when educated people cannot distinguish between a suspected qualitiative correlation (with no numbers whatsoever) and clairvoyance, it is saddening.
There are two consequences that I can see from this set of actions:
1) People are on guard for earthquakes (which is always good).
2) People start believing whatever an "authority" tells them is right, which is really lousy.
I think it's a given that anyone with a scientific mindset should look at such results with interest, but at the same time with caution and critical awareness. If Dr. Rahimi Tabar's correlation makes it through the scientific "prodding" process, nobody would be happier than me, but the way we treat science and its application in everyday lives and public policy is really important.