Maceió, September 16, 2019 -  Researchers from the University of Houston, one of the greatest geology centers in the world, revealed inconsistency in the interpretation of some methodologies used by CPRM (Geological Survey of Brazil) regarding the geological phenomena in the districts of Pinheiro, Mutange and Bebedouro, in Maceió. The researchers evaluated in detail the CPRM document and found that, besides the  imprecision regarding the methodology used, there are failures in the analysis of the maps that identified the instability in the soil and that the natural effects present in the region were disregarded by CPRM, among other points.

The team of geophysicists at the University of Houston conducted a series of studies to analyze the subsidence (slump) and the seismic events in the three districts of the city in Alagoas. In May this year, CPRM disclosed a preliminary report that indicated  salt extraction activity (the rock salt extraction) as the main cause of the phenomena observed in the region.

The University of Houston report indicates that CPRM used methodology that may have caused misinterpretation. For example, the government body drew conclusions about the condition of the caves using data that are unfit for the purpose. Besides, the researchers from the American university warned, while describing the interferometry work that analyzed the subsidence in the east margin of Lagoa Mundaú, that CPRM included an 'integration map of the soil instability processes". The map shows a subsidence that coincides with the area of the salt mines, but there is also a substantial deformation further to the south, distant from the salt extraction area. "This slump, outside the mines region, suggests a deformation mechanism not related to the salt extraction", indicates the American study.

Another important conclusion of the researchers was the study regarding the "signatures" of the seismic waves, which demonstrated that the quakes in the districts had natural origin. The Houston researchers identified "large amplitude of Lg wave and low amplitude of P waves resulting from the seismic tremor of March 3, 2018", confirming the event had a natural cause. CPRM had said in a report from May that "it is clear that the seismic source is close to the surface and it is not a tectonic event (i.e. natural) caused by a fault in the base".

Houston researchers have also used a supercomputer to make a three-dimensional modelling, simulating an eventual collapse of all the salt caverns in the region. The result was "67 times smaller than the subsidence measured by the interferometry, which is a great discrepancy", says the conclusion in the study. "This indicates that some other mechanism or mechanisms, not related to the brine cavities, might be the dominant cause of the subsidence".

However, the studies corroborated one of the CPRM's perceptions: that there must be many causes for the problem. Among these causes, says the American university, there is rainwater retention in the soil, which contributes to the instability of the land in Pinheiro, that is saturated with liquid, during the natural tremors. According to the study, the soil lubrification caused by the poor conservation of the drainage, sewage and supply systems of Pinheiro, associated to the natural geological faults of the subsoil, have worsened the damages caused in the streets and buildings by the densification of the terrain.

Braskem disagrees with parts of the analyses in the report presented by CPRM and understands that "so far, there is no technical evidence of the causes of the geological events in the districts, which is fundamental for the definition of strong solutions". Therefore, the petrochemical company has sought the opinion of researchers and experts for a better understanding of the phenomenon.

The University of Houston is an important center of geophysics and seismology research located at a city considered the world's technical center of the oil industry. In the state of Texas, there is significant salt exploration, as well as gas and oil exploration.

The professors who participated in the research have already worked for other   internationally-renowned institutions, like the MIT (Massachusetts Institute of Technology) and the University of California. Rob Stewart, coordinator of the research team, is a director at the Allied Geophysical Labs, with PhD in geophysics by the MIT, and  integrates the Texas Board of Professional Geoscientists. He is from Canada, a country with recognized experience in geology. The research had also the participation of professors Aibing Li (PhD in Geophysics by Brown University) and Yingcai Zheng (PhD in Seismology by the University of California).

The University of Houston report will be made available for the public agencies and competent authorities. The CPRM itself, in its report on the events in Maceió, indicated that new studies could be incorporated to the initial result for a better understanding of the factors that triggered the geological processes in the district of Pinheiro. "We believe that the studies and evidence presented may provide support for CPRM to fulfill its mission of improving the understanding of these matters and help in the search for a solution for the people and the city of Maceió", add the researchers in the study.