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The Moro Gulf Earthquake Research paper

The Moro Gulf Earthquake Research paper Chapter 1-5

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Earthquake Engineering (CE 407)

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Technological Institute of the Philippines

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Chapter 1

Introduction

12:11am, August 17, 1976, while the residents of the largest gulf in Mindanao

Island was sleeping (about 950 kilometers south of Manila), they have been shaken

by one of the unforgettable and powerful earthquake that happen in the Phillipines,

the midnight killer or also known as " The Moro Gulf Earthquake ". The movement

along the cotabato trench generated a catastrophic 8 magnitude earthquake with

intensity VII (Highest Intensity). It is known as the deadliest earthquake and tsunami

hit recorded to hit the Philippines in the last 40 years.

phivolcs.dost.gov/index.php/news/7643-prepare-for-tsunami-urges-usec-solidum

The location of the epicenter was the Moro Gulf (near Lebak, Sultan Kudarat)

that affects the Zamboanga del Sur, Maguindanao, North Cotabato, South Cotabato,

Lanao del Norte, Lanao del Sur, Sultan Kudarat and the Basilan, Sulu and Tawi-Tawi

islands, and the cities of Cotabato, Zamboanga and Pagadian. Approximately

120,000 peoples are affected by this disastrous event. Livelihoods and industry

buildings has been destroyed completely.

Source: Rappler

The Moru Gulf Earthquake known as one of the largest and deadliest

earthquake that occurs in the Earth. It is said that it is not associated in the Philippine

trench but with a much less prominent trench system in the North Celebes Sea, the

south of Mindanao. Moreover, the seismicity is at depths greater than 500 km

according to the data (Cohn 1979). In addition, the largest aftershock (with a

magnitude of 6) occurred outside the main aftershock area after 12 hours and

evidently resulted from motion on a subsidiary fault since the P-wave first motion

data indicate strike-slip motion for this event.

COTABATO CHINESE SCHOOL

GYMNASIUM

ADMINISTRATION BUILDING

HARVADIAN COLLEGE

NOTRE DAME UNIVERSITY

THE ADMINISTRATION

BUILDING

THE AUDITORIUM AND

SCIENCE BUILDING

THE NEW RESIDENCE HALL

THE TECHNICAL SCHOOL

DAWNS HOTEL

D’MAX RESTAURANT

IMPERIAL HOTEL

MELBOURNE HOTEL

NEW SOCIETY HOTEL

SAGUITTARIUS HOTEL

SULTAN HOTEL

COTABATO CINEMA

FRANCEL THEATER

RITA THEATRE

IMMACULATE CONCEPTION

CHURCH

TAMONTAKA CATHOLIC

CHURCH

AMICUS BUILDING

BOSTON BAKERY

COTABATO AUTO SUPPLY

COTABATO FIRE and POLICE STATION

FIRST GIFT AND BOOKSTORE

LCT HARDWARE AND AUTO SUPPLY

MELINEEN BUILDING

SOUTH SEAS TRADING

TAN BO BUILDING

TISON BUILDING

WATERFRONT WAREHOUSES

QUIRINO BRIDGE

TAMONTAKA BRIDGE

ZAMBOANGA CITY

PAGADIAN CITY

The Moro Gulf Earthquake is considered as one of the world's deadliest earthquakes.

“The 1976 August 16 Philippine earthquake thus represents the first clear seismic evidence for a north-east dipping subduction zone beneath Mindanao in the Moro Gulf, North Celebes Sea.”

Chapter 3 Contributing Factors to Seismic Vulnerability

In this chapter, seismic vulnerability of buildings, located near the islands of Mindanao and Sulu, affected by the most recent earthquakes that occurred in Cotabato City, are presented. Seismic vulnerability influences how damage caused by an earthquake in each area is assessed from a construction point of view. The causes of high vulnerability even at very low levels of seismic forces may be different due, for instance, to structural irregularities, inadequate design, poor quality of materials, absence of constructive details, and scarce maintenance (Krstevska et al., 2010; Betti and Vignoli, 2011; Milani and Valente, 2015a; Clementi et al., 2017a,b; Fonti et al., 2017; Formisano et al., 2017, 2018; Milani et al., 2017a; Valente et al., 2017; Luchin et al., 2018; Valente and Milani, 2018a,b,c).

SITE CONDITIONS AND SOIL EFFECTS

The majority of Cotabato City's historic district is barely a few feet above sea level. By filling, the city's overall level was raised by one meter. This area of the city is built on deep, relatively new deltaic deposits. Engineer Augusto Chio said that a digging in this location that went to a depth of nearly 90 meters did not hit hard material.

Table 5, which contains simplified driller's logs of many wells recently drilled for water supply purposes, provides a rough sense of the subsurface materials of the low-lying area. The wells are southwest of the Notre Dame University Campus, as illustrated in Figure 3 by Buildings I, 2, 3, and 4. Table 6 contains a list of structures whose positions are depicted in Figure 3. Manuel D. Magdael and Lauro S. Gecosala, Sr. of the Office of the City Engineer contributed the information. Colina Hill, a worn limestone hill about 55 meters high, sits immediately to the south of the city centre and once housed the Army Headquarters.

compared with damage on very firm ground of high strength and density. The contrast is seldom pronounced when the range of soil involved goes only from intermediate to firm without the presence of soil of such very denseness and strength like that in Cotabato City.

One can only speculate on the reason for the apparent amplification of surface ground motion on the low-lying land in the absence of borings penetrating to bedrock, with associated soil properties including shear wave velocity, and in the absence of strong motion accelerograms on Colina Hill and middle sites (or anywhere else for that matter). Because the researchers found only some evidence of building foundation displacement, it appears that the effect was one of amplification rather than liquefaction. However, the action described could also be attributed to the lurching or horizontal land sliding of pockets of the foundation soil's bottom strength.

STRUCTURE OBSERVATIONS

The ground motion characteristics at Cotabato City were controlled by the conditions: 1) a Magnitude 8 earthquake; 2) an epicentral distance of 100 km, and 3) a distinct variation in local site conditions. These conditions were dominant factors influencing the following points concerning the damage:

All damage was concentrated on the soft marshy soils.
The magnitude of an earthquake cannot by itself be an indication of the extent or severity of damage that may be expected.
All collapses of concrete buildings, although on small wood piles, were strongly affected by increased ground shaking due to soft foundation materials.

The practice in building and bridge design and construction had a strong influence on the structural performance during the earthquake. The points concerning practice which the EERI team found to be important are:

Reinforced concrete buildings can be designed to behave satisfactorily during an earthquake. An example of satisfactory design and performance is the Tison Building.
Large torsional eccentricities caused some buildings to fail. They were not designed to resist seismic torsional forces
Reinforcement detailing was done without apparent consideration of load paths in the structure and elements. Among the serious problems noted were a) splicing of column reinforcement below the soffit of the beam, b) cast iron downspouts in the columns and joints (Figure 117 and Figure 118), c) excessive column tie spacings not based on seismic shear and confinement requirements, and d) beam reinforcement not anchored for seismic building response.
Concrete strength tests were not required for all buildings
It is a common practice in Cotabato City, as it is throughout the Philippines, to construct exterior walls, as well as interior partitions, out of masonry. Infilled within a frame, these walls tend to stiffen the frame line and therefore attract seismic loads. Since the walls contain little, if any, reinforcing steel, the walls explode. The loads immediately overstress the frame, causing it also to fail.

4 Important Events

Since 1972, the Philippines has been under "martial law," however the typical functions of civil administration are now carried out by civilians rather than military troops. However, President Ferdinand Marcos, with the support of the military, sets policy on practically all major issues. Furthermore, rather of being elected, the President appoints key executives, including mayors. Authority relationship has been in effect for years causing to have a doubt on who would make important decisions and enunciate policy.

Most roads in Cotabato City were cleared of rubble within 10 days. For 3 hours, the long-distance service was out while the local phone system was never inoperative. School building suffered a severe damage causing for a suspension of classes aside from the trauma dealt by the earthquake on the locals. In the devastated portions of the city, the earthquake resulted in a power outage. All of the local radio stations were shut down. Under such circumstances, communicating with the public would be tough. Guns were fired into the air frequently shortly after the earthquake. There were apparently various explanations for this. One was to scare away any rebels who might try to take advantage of the earthquake's potential for disarray. The second reason was to wake people up in order to warn them about the dangers of aftershocks. Shortly after the guns were fired, vehicles with loudspeakers were dispatched throughout the city to warn residents of the danger of aftershocks, to advise them to get outside and away from buildings (normally, the curfew would prevent such action), and to announce the declaration of an official "state of calamity”. In the Philippines, it appears that the military has complete control over all topics of public concern in the case of a "state of calamity." Soon after the earthquake, President Marcos decided not to seek help or accept aid from foreign countries resulting in scarcity of food supplies.

Chapter 5

Lessons Learn and Recommendations

5 Lessons Learned

We can't prevent natural disasters from wreaking havoc, but we can mitigate their impacts. The sharing of crisis management stories is an effective learning tool. Hearing from others who have lived through disasters might help you make better decisions about your own readiness while planning for the worst-case situation. Information regarding catastrophe hazards should be broadcast on television or radio stations to help people prepare before and during disasters. Our group prepared few takeaways from the 1976 Moro Gulf Earthquake.

5.1 Dwellings must be at least 200 meters inland

The tsunami was responsible for ninety percent of the deaths in Moro Gulf earthquake. Moslem communities were hardest damaged, as most of the homes were built on piling in the sea or were close to the shoreline. The high number of deaths in these areas is due to a lack of awareness of the region's potential for earthquakes and tsunamis. Despite the fact that a 5 to 15-minute period passed between the earthquake and the arrival of the tsunami waves in some regions, residents in the area did not seek higher ground following the earthquake and instead stayed in their homes.

5.1 Early warning saves lives

Since the Philippines was under the martial law that time, the top administrator including the governors, mayors was personally appointed by Marcos rather than being elected. And because of this authority relation, there was no- warning disaster strike.

5.1 Early Communication

Communications within the military throughout the nation were never impaired. As is so often the case during the emergency period following a large -scale disaster, radio-equipped vehicles (both government and private) played a crucial role in reconnaissance for early damage assessment and in the coordination of emergency actions

To raise awareness and prepare a bigger group of people, disaster management training should be provided in schools, workplaces, and organizations. The vast majority of people should be taught on how to react in the event of a calamity. If done correctly, the basics of ducking, covering, and holding could save anyone's life during an earthquake. Furthermore, having insurance coverage might help you lessen the loss and overcome the issue more quickly.

References:

PHILVOCS (Sept 8, 2021). “ Historical Earthquake”. Retrieved from: phivolcs.dost.gov/index.php/earthquake/destructive- earthquake-of-the-philippines/17-earthquake? fbclid=IwAR0x5nSrJzjS4Xz9P_Wq9- c8gvmMQ9OIGi7_Nild7zsP3RyN7V09xoIgvYg

Haas, J (1978). “ The Philippine Earthquake and Tsunami Disaster: A Reexamination of Behavioral Propositions”. Disasters, Vol. 2, No. 1, pp. 3-1 1. Retrieved from: onlinelibrary.wiley/doi/pdf/10.1111/j.1467- 7717.1978.tb00055#:~:text=The%20epicenter%20was%20in %20Moro,Pagadian%20City%20on%20the%20North.

USGS (2021). Today in Earthquake History. Retrieved from: earthquake.usgs/learn/today/index.php? month=8&day=16&submit=View+Date

Cohn S., Gordon S. (1979 ) “The 1976 August 16, Mindanao, Philippine earthquake (Ms = 7) - evidence for a subduction zone south of Mindanao .” Geophysical Journal International, Volume 57, Issue 1, April 1979, Pages 51– 65. Retrieved from: academic.oup/gji/article/57/1/51/

Baldillo V. (1978). “ The Mre Gulf Tidal Wave of 17 August 1976”. Philippine Studies 26 (1978): 426 - 436. Retrieved from: jstor/stable/

Fabbrocino, F., Vaiano, G., et al. (1AD, January 1). Large Scale seismic vulnerability and risk of Masonry churches IN Seismic-Prone Areas: Two TERRITORIAL case studies. Frontiers. Retrieved from: frontiersin/articles/10.3389/fbuil.2019.00102/full.

Stratta J., Duke M., et al. (1977). MINDANAO, PHILIPPINES EARTHQUAKE. NEHRP Clearinghouse. Retrieved from: nehrpsearch.nist/

(2021). Retrieved 8 September 2021 , from phivolcs.dost.gov/index.php/earthquake/destructive- earthquake-of-the-philippines/17-earthquake?fbclid=IwAR2RCV9Lvpp2yw- iA9D-4hgzAu7d6tc8KNQhmaRKO1zR4jUZg_2xtptL8BA

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