Blogger’s Note: The writer below whose credential as a Seismic Engineering Consultant for Nonstructural Hazards Mitigation and Earthquake Hazards Reduction Program answers the most often asked questions thrown in by the many readers of this blog. He is well known in his circle and, in the span of his career, has authored the following Seismic Engineering Articles:
• NONSTRUCTURAL HAZARDS MITIGATION – SEISMIC HAZARDS REDUCTION PROGRAM
“The Present Status In The Philippines – Part 1 & Part 2.
• EARTHQUAKE PROTECTIONS FOR THE LIQUEFIED PETROLEUM GAS INDUSTRIES.
• EARTHQUAKE PROETCTIONS FOR THE HVAC / MEP INDUSTRIES.
• EARTHQUAKE PROTECTIONS FOR THE FIRE PROTECTION INDUSTRIES.
• STRONG-MOTION SEISMIC INSTRUMENTATION FOR BUILDINGS (Pattern from the
United States Geological Survey & California Strong-Motion Instrumentation Program).
Engr. Limeta first corresponded with this blogger here.
* * *
Dear Mr. TULISANES,
If I am not mistaken, I read on your wonderful website that your mapping concerning the exact location of the West Valley Fault System is being referenced from PHIVOLCS. Please, advise me immediately and please correct me if I am wrong. If it is referenced from PHIVOLCS data, it is outstanding.
Without a doubt, PHIVOLCS has a team of highly-educated, highly-experienced, and highly-trained Geologists (Volcanologists / Seismologists) and could be some are Geo-Technical Engineers. We must be very thankful to the professionals of PHIVOLCS, led by their director.
In fact, I am using various seismic data and seismic hazard maps of PHIVOLCS and I am using it as my utmost references in the field of Seismic (Earthquake) Engineering. PHIVOLCS is an expert for Geo-Hazards Analyses.
If your mapping of the existing West Valley Fault System trailing within the heart of Metropolitan Manila whether highly-accurate or less-accurate, is still a good source of technical information. In-case, your mapping of the West Valley Fault System is less-accurate (IPAGPALAGAY LANG PO NATIN), still the existence of the West Valley Fault System is a posing DANGER if it is trailing within the heart of Metropolitan Manila. Therefore, I support your mapping all the way and in-fact I consider you as one of the genius in tracking and mapping fault lines, meaning to say you are providing data which are reality we have to accept. Major Earthquakes are real and the existence of the West Valley Fault is real whether we like it or not.
According from my colleague (Carl L. Strand, M.S. Geology – President of the Strand Earthquake Consultants, Los Angeles, CA. U.S.A.) “THERE IS NO PANACEA AGAINST MAJOR EARTHQUAKES.”
What is the minimum distance that a house or building should be from a fault line to be considered safe ?
According to Paterno Esmaquel II of GMA News (March 14, 2011 / 8:31 A.M.), PHIVOLCS stated “Constructions Must Also Make Way For A 5-Meters Buffer Zone On Both Sides Of An Active Fault.” In Port-au-Prince in Haiti, the capital and the population is over 150,000 perished due to Earthquake Magnitude 7.0 in 2010 despite the area is 25-Kilometers away from the active fault that caused the disaster.
July 16, 1990 Luzon Killer Earthquake measured 7.8 Magnitude in the Richter Scale (Ri = 7.6 Magnitude), produced 125-Kilometers ground rupture that stretched from Dingalan, Aurora to Kayapa, Nueva Ecija, movements along the Philippine Fault and Digdig Fault. The epicenter is in Rizal, Nueva Ecija northeast of Cabanatuan City. Yet, Baguio City was devastated and many were asking, how many kilometers is Baguio City away from Rizal, Nueva Ecija ?
Let us use the 1997 Uniform Building Code as our reference. Because, this Building Model Code has requirement for “Distance To Nearest Seismic Source.”
Ø Seismic Zone 4
Ø Effective Peak Ground Acceleration = 0.40 g
Ø Soil Profile = Class B (If Unknown = Class B As Default)
Ø Seismic Source Type = A
Ø Near Source Factor and Seismic Coefficients depends on the following :
Less Than 2-Kilometers
More Than 15-Kilometers
Seismic Source Type A “Faults that are capable of producing large magnitude events and that have a high rate of seismicity – Magnitude greater than 7.0.” According to PHIVOLCS, West Valley Fault is capable to unleash Major Earthquake with 7.2 Magnitude in the Richter Scale.
In short, the nearer a house or a building to the existing Fault Line or Seismic Generator, the stronger the magnitude and the severity of the Intensity is high. The further a house or a building to the existing Fault Line or Seismic Generator, the weaker the magnitude and the Intensity is lower.
Therefore, it is my humble opinion that 5-Meters may not be sufficient. Yes, my humble opinion for everybody is entitled to his / her own opinion. Therefore, I am not in the proper position to specify what will be the established Minimum Distance For A House or Building Away From The Existing Fault Line. Our government authority should be the one to establish the above mentioned safe distance.
Where or what is the safest place to be in Metro Manila as regards getting less damage from a 7.2 Magnitude Quake ?
This is a very difficult question to answer. During Major Earthquake event, expect the unexpected. Until now, Geologists, Seismologists, Seismic (Earthquake) Engineers, and to include Geo-Technical Engineers around the world are still studying and analyzing the characteristics and behaviors of earthquakes.
A modern-day building structure which are strongly-built and designed to withstand Intensity X or higher (0.55 g and higher than 1.0 g Peak Ground Acceleration) may survived or may not survived particularly if the areas were studied by experts to experience POTENTIAL LIQUEFACTION by weakening its structural foundations, it may tilt, partially collapse, or total collapse. Potential Liquefactions are those areas near seashores, rivers, lakes, or reclamation areas. Potential Liquefaction will make the soil “SOFT” and no longer stiff where the structural foundations of the buildings and other structures will become weak. In 1964 Niigata Earthquake in Japan measured 7.6 Magnitude, the strongly-built buildings tilted and other toppled to the ground due to Earthquake Generated Ground Liquefaction.
The 1999 Taiwan Earthquake : On September 21, 1999 an earthquake measuring 7.6 Magnitude in the Richter scale shook the city of Taichung, Taiwan, killing 2,375 people. The epicenter was near Nanto, and 145-Kilometers south-southeast of Taipei. The quake toppled 13,000 high-rise apartments. It appears that the only buildings that suffered total collapse from this earthquake were low-rise masonry structures.
The safest place in Metropolitan Manila are those houses or buildings furthest away from the Valley Fault Systems, houses and buildings established by Geo-Technical Engineers where Potential Liquefaction will be low, those far away from sea-shores, rivers, lakes, or reclamation areas. Geo-Technical Engineers are experts on the subject of Ground Liquefaction. Buildings and houses having structural foundations within stiff-grounds. That is why in the seismic provisions of the applicable Building Model Codes & Standards, Site Soil Class are being specified.
Old buildings, old historical buildings / other old historical structures, dilapidated buildings, and to include old residential houses may not survive near the existing fault line or even far away from the existing fault line. We may ask the Geo-Technical Engineers and Geologists and they will agree.
How do high rise buildings, especially condos, behave during earthquakes ?
During Major Earthquake event, high-rise buildings will drift back and forth for several cycles. The Design Structural Engineers are expert professionals concerning the movements of the buildings due to wind and seismic loads. During earthquake, seismic lateral forces will be applied to the high-rise buildings. The high-rise buildings will drift (Inter-Story Drift / Maximum Allowable Drift) from ground floor to roof-deck based on the Maximum Inelastic Response Displacement Analysis.
The highest Acceleration g will be felt at the highest part of the building and the lowest Acceleration g will be felt at the lowest part of the building. However, modern-day high-rise buildings designed and built in accordance to the applicable Building Model Code have very strong structural elements known as Moment-Resisting Frames which will resist applied seismic lateral forces in any direction and also capable to resist potential torsional movement as being stipulated by the ASCE 7-05 / ASCE 7-10 “Minimum Design Loads For Buildings & Other Structures.”
High-rise buildings and low-rise buildings will resist displacement at the base of the building known as Building’s Design Base Shear.
During Major Earthquake event, a series of strong-motion low-frequency sinusoidal waves of varying magnitude are travelling under the earth’s ground surface. The established earth’s natural ground periods are ranging from 0.2 Second up to 1.0 Second (5.0 Cycle up to 1.0 Cycle). Low-rise buildings usually have fundamental period of less than 0.70 Second and high-rise buildings usually have 1.0 Second or higher. Although, the buildings may damp the earthquake generated ground shakings (let us say 5% Damping). If the earth’s natural ground period will resonate to the building’s fundamental period, there will be a strong tendency that the buildings will suffer severe structural damages.
Worldwide experienced (countries having Major Earthquake disturbances), low-rise buildings collapsed during Major Earthquake event and that high-rise buildings survived. One of the technical / engineering reasons is that, high-rise buildings have a very high fundamental period in Second way above 1.0 second plus damping capability will not potentially resonate to the earth’s natural ground period.
Also, worldwide experienced (countries having Major Earthquake disturbances), modern-day high-rise buildings and strongly-built in accordance to the provisions of the applicable Building Model Code survived aftermath of Major Earthquake and that low-rise buildings survived, others were severely damaged, others totally collapsed, and low-level residential houses were severely damaged, the Americans, Japanese, Taiwanese, New Zealanders, Turkish, Chileans, Mexican, and others knew this issue.
High-rise building’s structural elements are strong and survived aftermath of Major Earthquakes, but the Nonstructural Elements were severely damaged, such as Equipment * Component * Systems. Like Automatic Fire Sprinkler Piping Systems, HVAC / MEP Systems, and the Hazardous Piping Systems carrying fuel gases like LP-Gas created building fires.
One of the most damaging occurrences aftermath of Major Earthquake event is a Large-Scale Metropolitan “FIRE FOLLOWING EARTHQUAKE.” According from the American Society Of Civil Engineers (ASCE) and the Risk Insurers.
My shared seismic info herein shall not prevail as precisely accurate. Again, during Major Earthquake event, EXPECT THE UNEXPECTED. About Major Earthquakes, no one knows when will it strike, where will it strike, how strong will it be, but surely it will happen any moment without signs and warnings. Therefore, Earthquake Preparedness & Hazards Mitigation Programs shall be implemented.
Designs and constructions of new buildings (structural elements), including proposed site location shall be in accordance with the provisions of the applicable Building Model Codes, Authority Having Jurisdiction (AHJ), proposed site location shall be brought to the attention of the Building Officials, site soil profile shall be analyzed thoroughly by the Geo-Technical Engineers.
Nonstructural elements within the buildings such as Equipment * Components * Systems shall be designed, constructed, and installed in accordance with the seismic provisions of the applicable Building Model Codes & Standards.
Example : Earthquake Protections intended for the Automatic Fire Sprinkler Piping Systems / Fire Suppression Systems within high-rise buildings and low-rise buildings were not provided, it is a direct violation of the Building Model Codes & Standards, such as the 2007 – 2010 NFPA-13 Standards.
The structural integrity of very buildings or structures if safe to be occupied before, during, and aftermath of Major Earthquake event should be brought to the utmost attention of the Design Structural Engineers.
Major Earthquake is part of nature, the Japanese learned to live with it. Even the most advanced and industrialized nations (wealthy nations) like United States, Japan, Taiwan, New Zealand, and others having extensive earthquake protection and hazards mitigation programs and their buildings, facilities, other structures are truly 100% Code & Standard Compliant, still they experienced wide-scale devastations.
In an event of a Major Earthquake, the people are in the mercy hands of GOD.
In Book Of Job 9 : 5 – 6 “He moves mountain without their knowing it and overturns them in his anger. He shakes the earth from its place and makes its pillars trembled.”
Should you have further questions, please always feel free to communicate with me.
Bobby G. Limeta
Seismic Engineering consultant
Nonstructural Hazards Mitigation
Earthquake Hazards Reduction Program