Philippine Standard Time
 
facebook facebook facebook
COMPILATION OF DAMAGING EARTHQUAKES OF THE PHILIPPINES
Palimbang Earthquake - 06 March 2002

Summary of the event:
Ma. Leonila P. Bautista and et al.

 

The earthquake occurred on March 6, 2002 at 05:15 am (local time). Its epicenter as located by PHIVOLCS is at 6.1 N; 124.0 E; 81 km or about 81 km SW of Isulan, Sultan Kudarat. PHIVOLCS computed its depth of focus at 15 km. Its surface magnitude was computed by the Pacific Tsunami Warning Center as 6.8 while its moment magnitude (Mw) and body wave magnitude (mB) were computed by the the U.S. Geological Survey (USGS) as 7.2 and 6.3, respectively. Based on the earthquake location and mechanism solutions, its source is attributed by PHIVOLCS to subduction along the Cotabato Trench.

Fig 1. Shows the PHIVOLCS earthquake bulletin for this event.

 

As of March 9, 2002, the Office of Civil Defense (OCD) records show that 8 people had died and 41 were injured due to the earthquake. It affected 7,684 families in the provinces of Sultan Kudarat, Sarangani, North Cotabato and South Cotabato including four cities and 17 municipalities (OCD Memorandum dated March 9, 2002). The quake damaged 4 road networks, 7 bridges, 36 school buildings, 29 business establishments, 1 megadike, 2 health centers and 17 public buildings. Damage amounted to 4.175 million pesos or about 80,000 US dollars.

The focal mechanism as determined by Harvard University (Figure 2a) is underthrusting along a NW-trending plane with minor strike-slip component. The strike conforms to the established trend of the trench. The USGS's solution for the event (Figure 2b) shows an almost similar mechanism with a slightly larger strike-slip component than the solution of Harvard University.

Fig 2a. Focal Mechanism of the earthquake as determined by Harvard University

Fig 2b. Focal Mechanism of the earthquake as determined by USGS.

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division

Historical Seismicity:

 

Based on the PHIVOLCS catalog, the area is characterized by moderate to high intensity (Figures 3a and 3b) as shown by seismicity plots for the last 100 years. The location of the 2002 event is very near the location of the 1976 Ms 7.9 event.

click for a higher resolution

Fig 3a. Seismicity of Mindanao for the last 100 years. Arrows point to the locations of the 1976 and 2002 earthquakes (source: PHIVOLCS catalog)

 

click for a higher resolution

Fig 3b. Earthquakes with Ms 6.5 and above and depths 0-100 km for the last 100 years (source: PHIVOLCS catalog)

 

The quake's source region, the Cotabato Trench, is an active N- to NE-dipping subduction zone system whose slab has been traced down to 150 km deep based on earthquake data (B. Bautista, 1996). Figure 4a shows a section called N-N’ that traces the trend of the trench based on seismicity data. The figure also shows the slab to be moderately-dipping while a cluster of hypocenters are found at 0-100 km depth. Figure 4b shows the location of section N-N’ where the seismic cross section (section N-N’) was cut. The trench's past movement had caused large magnitude earthquakes to occur such as the August 17, 1976 Moro Gulf Earthquake that killed more than 3000 people due to high tsunami waves that swept many towns facing the Moro Gulf including Cotabato and Pagadian Cities.

 

click for a higher resolution

Fig 4a. Downgoing slab of the Cotabato Trench (labelled CT) as defined by seismicity data (after B. Bautista, 1996)

 

click for a higher resolution

Fig 4b. Map showing the location of line N-N’, the cutting plane used for Figure 4a (after B. Bautista, 1996)

 

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division

 

Impacts:

 

The quake's ground shaking intensities at various places were estimated using the Fukushima and Tanaka's attenuation (1990) relation (Figure 5). The highest intensity is estimated to be Intensity IX in the epicentral region specifically in the town of Palimbang in the province of Sultan Kudarat. The quake was estimated to have been felt at Intensity VIII in the town of Maitum in the province of Sarangani and in the town of Lebak of Sultan Kudarat province. Meanwhile, the observed intensity reports are shown in Figure 6 and are based on actual reports of PHIVOLCS field stations, Office of Civil Defense and the mass media.

click for a higher resolution

Fig 5. Predicted isoseismal map using Fukushima and Tanaka's attenuation model (1990) and Gutenberg and Richter's intensity-acceleration relation.

 

click for a higher resolution

Fig 6. Isoseismal map of the event. Intensity reports based on actual accounts.

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division

Tsunami Model:

 

Dr. Yuchiro Tanioka, PHIVOLCS JICA Expert, modeled for the possible tsunami generated by the event. He computed for a possible 3-m high tsunami in the town of Palimbang in the province of Sultan Kudarat. Based on the modeling results, the value progressively decreases from said point till it reaches to only about 30 cm at Lagung Point in Maguindanao province NW of Palimbang and about 1 m in the town of Kiamba, east of Palimbang. Dr. Tanioka also modeled the tsunami waves at 1, 5 and 10 minutes after the earthquake. The 1-minute map (Figure 7a) indicates a recession of sea water, the results of which are consistent with the observations of the local people. Likewise, the 5- (Figure 7b) and 10-minute (Figure 7b) maps show that waves had already came back to inundate the shore five and ten minutes after the main shock.

 

Fig 7a. Model of tsunami waves one minute after the main shock (after Y. Tanioka, 2002). Blue shaded areas show the location of areas where recession of water is expected. Eyewitness accounts in the town of Palimbang in Sultan Kudarat and in Maitum and Kiamba towns in Sarangani province conform to the results of the model.

 

Fig 7b. Model of tsunami waves five minutes after the main shock (after Y. Tanioka, 2002). The figure shows that five minutes after the main shock, the water has already rushed back to the shore. Again, this is consistent with the eyewitness accounts.

 

Fig 7c. Model of tsunami waves10 minutes after the main shock (after Y. Tanioka, 2002)

 

Meanwhile, the Pacific Tsunami Warning Center (PTWC) issued a tsunami bulletin at 5:41 AM that stated that "no destructive Pacific-wide tsunami exists" (Figure 8). This was received at PHIVOLCS at 6:42 AM by fax. Since the area affected was in the Celebes Sea and away from the Pacific Ocean, the PTWC bulletin was quite accurate.

 

Fig 8. Copy of the fax sent by the Pacific Tsunami Warning Center (PTWC) to PHIVOLCS by fax.

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division

Actual Observations:

 

1. Palimbang, Sultan Kudarat

Palimbang is a coastal town of 40,000 people (NCS), 1995). In this place, a concrete chapel collapsed due to intense shaking (PHIVOLCS QRT Report). No one died as a result of the collapse because the church has previously been abandoned due to military operations in the area. However, one person was reported dead and seven wfrom Barangays Poblacion, Badiangan and Colubo were injured. Two people were injured and were hospitalized (OCD Region XII, March 9, 2002). General Magsino reported to PHIVOLCS Main Office that the sea was observed to have receded 150 m from the shoreline. It then went back 75 m inland damaging two boats (General Magsino and PHIVOLCS QRT Report).

 

2. Maitum, Sarangani

Maitum (pop: 35,000) is the neighboring town of Palimbang. It belongs to the province of Sarangani province. The highway linking Maitum and Palimbang and places in Barangays Pinol and Lipo were affected by landslides. A repeater antenna fell. A Baptist Church and a water tank tilted. In Barangay Mabay and Sitio Talikod, three sandboils measuring 8-10 cm wide and 12 cm deep were observed. Cracks on the ground measuring 5-10 cm wide, 2 cm deep and 30 cm long were observed at Sitio Saub in Barangay Mabay and in Nolasco St. Water was observed to have receded 300 m. A pumpboat was totally damaged and dead fish were observed soon after (PHIVOLCS QRT Report). Two persons died at Barangay Mabay due to falling hollow blocks while five others were injured in Barangays Kawa, Old Poblacion and Kiambing (OCD Region XII, March 7 and 9, 2002). One church, eight houses, a school stage and a five-span concrete fence of Rude Elementary School were totally damaged (OCD Region XII, March 7, 2002). One convent, 18 houses, a water reservoir, the Edenson Mission College Building and two business establishments were partially damaged (OCD Region XII, March 7, 2002). A vehicle and two fishponds were damaged (OCD Region XII, March 7, 2002). About 10,000 people were evacuated (OCD Region XII, March 7, 2002) and stayed in schools and gymnasium (Ms. Fe Falgui, local resident (083) 509 4038/509 4028).

 

3. Kiamba, Sarangani

Kiamba (pop: 39,000) is the next shore town after Maitum. Two public markets made of wood located in Barangay Kiamba and Lagundi collapsed. A local resident described the quake as very frightening and "parang hinahalungkay galing sa ilalim" (Ms. Fe Falgui, local resident (083) 509 4038/509 4028). The Sarangani Cable Office was totally damaged. Walls of several houses collapsed leaving only posts and beams behind. Two walls in two classrooms of the Suli Elementary School fell. At the Southern Cotabato Academy and at the Bagtasan Elementary School, a fence and a wall collapsed, respectively. Three churches sustained slight damage. Ten houses were partially damaged while five houses built in 1976 were totally destroyed. Piles of softdrink bottes toppled down. Cracks were observed along downtown Kiamba. Tual Bridge sank by 6 cm. Water pipes were destroyed. Thirteen persons from Barangays Nalus, Suli, Poblacion, Laabuk-Tual, Kling, Tablao, Tual, Lagundi, Kapate and Tabak-Tual were injured (OCD Region XII, March 7 and 9, 2002; PHIVOLCS QRT Report). Water receded 5-8 m three times (Mr. Rommel Palge, local govt ofc (083) 509 4038). Afterwards, water was again observed to rise (Mr. Leonardo Esteban, local resident (083) 509 4069). As a result, people went up the mountain. As of 1 PM of March 7, the Mayor of Kiamba refuses to allow people to return back to their homes. NDCC requested for an advisory from PHIVOLCS that it was safe to go back to their homes. About 32,000 people or more than 80% of its local population were evacuated at the Tumadang Elementary School and Iglesia ni Cristo Church (OCD Region XII, March 7, 2002).

 

4. Maasim, Sarangani

Maasim (pop: 32,000) is the next town after Kiamba following the highway. A four-span school fence of San Felipe Central Elementary School located in Barangay Colon collapsed (PDCC Alabel; (OCD Region XII, March 7, 2002). Three houses in Barangay Tinoto and Lomatil were partially damaged (OCD Region XII, March 7, 2002; PHIVOLCS QRT Report).

 

5. Alabel, Sarangani

Alabel (pop: 46,000) is the capital of Sarangani province. A child died when hollow blocks fell on him while another one man died at the time of the ground shaking (Source: Ms. Gay Melani Palma of DSWD Alabel tel no. (083) 508 2177 as relayed by Mr. Milo Tabique of PHIVOLCS Kidapawan Station).

 

6. Glan, Sarangani

Glan (pop: 74,000) is another coastal town along Sarangani Bay. In this place, a big rock fell disrupting traffic. Landslides were also reported in Barangays Kapatan and Alegado (OCD Region XII, March 7, 2002; Malaya, March 7, 2002). A bridge collapsed in Barangay Small Margus isolating the barangays of Batulaki, Kaltuad and Santo Nino (OCD Region XII, March 7, 2002). The quake caused a one-m wide depression on the concrete road at the Glan subport (Philippine Daily Inquirer, March 7, 2002). A mosque in Barangay Burias and a Barangay Multipurpose hall at Barangay Baliton collapsed (OCD Region XII, March 7, 2002). An old school building in Barangay Kapatan was totally damaged (OCD Region XII, March 7, 2002).

 

7. Bula, Sarangani

An undetermined number of residents were evacuated to higher grounds (Malaya, March 7, 2002).

 

8. Malapatan, Sarangani

Malapatan (pop: 48,000) is the next town NE of Glan. Landslides were reported by the Office of Vice Governor)

 

9. Lutayan, Sultan Kudarat

In this town of 34,000 people, a market collapsed (Malaya, March 7, 2002; OCD Region XII, March 11, 2002).

 

10. Isulan, Sultan Kudarat

Three houses in Kolambog, seven houses in Barangay Tayugo, Barangay Hall in Kolambog, a Catholic Church in Barangay Kalawag were partially damaged (OCD Region XII, March 11, 2002). The public market building in Baraangay Kalawag, municipal hall building in Barangay Kalaaawaag II and the department store building in Kalawag III sustained cracks (OCD Region XII, March 11, 2002). The fence of barangay plaza in Kolambog was damaged (OCD Region XII, March 11, 2002).

 

11. Tacurong City

A 74-old man in Barangay Baras died of heart attack during the earthquake (OCD Region XII, March 7 and 9, 2002; Philippine Daily Inquirer, March 7, 2002). The walls of 14 houses in the LGU Resettlement Project in Barangay San Pablo cracked (OCD Region XII, March 7 and 11, 2002). One house in Barangay San Rafael and one church in Barangay New San Isabela were damaged (OCD, March 11, 2002).

 

12. Surallah, South Cotabato

Surallah (pop: 62,000) is a town in Allah Valley located in the lowlands after the Sarangani mountain range. In this place, a house collapsed (Source: DSWD Alabel as relayed to Mr. Tabique of PHIVOLCS Kidapawan Seismic Station) and 158 others were damaged (OCD, March 11, 2002). A hanging bridge at Barangay Buenavista and a megadike at Barangay Centralla were partially damaged (OCD Region XII, March 7 and 11, 2002). Two were injured, one of them due to burns sustained while cooking (OCD Region XII, March 9, 2002). 274 families from the barangays of Lamsugod, Buenavista, Tubi-Allah, Veterans, Moloy, Duengas, Lolongbasing, Dalaay, Talahik and Central were affected (Provincial Disaster Coordinating Council, March 11, 2002).

 

13. Koronadal City, South Cotabato

Koronadal (pop: 118,000) is the capital of South Cotabato and is found NE of the town of Surallah after the Roxas Mountain Range. Two classrooms of the Barangay Cacub Elementary School and the stage of the Siodina Elementary School Building collapsed. (OCD Region XII, March 7, 2002). The firewall of the Agreda Station and that of the Multipurpose Building of Barangay San Roque also collapsed (OCD Region XII, March 7, 2002). The NDMU Dormitory and 10 m of its concrete fence facing the DPWH Building collapsed (OCD Region XII, March 7, 2002). A 25-m portion of the wall of the LAPCO Warehouse collapsed (OCD Region XII, March 7, 2002). 15 other houses either collapsed or were damaged (OCD Region XII, March 7, 2002). The Masagan Bridge, concrete bridge and walls of Barangay Saravia Elementary School at Barangay Saravia, the approach of the Ferry Bridge, the San Roque Elementary School in Barangay San Roque, the MSST College of Technology Building, the KCC Mall, the overpass of the South Cotabato Provincial Hospital and the Elan Building suffered cracks (OCD Region XII, March 7, 2002; Malaya, Philippine Daily Inquirer and Manila Bulletin, March 7, 2002). The same were sustained by the walls of the Dungan Elementary School, Mangga Elementary School, Marbel 8 Elementary School, Mambucal Primary School, Mercury Drugstore and Chiu Kim Building (OCD Region XII, March 7, 2002). Two posts of the South Cotabato Electric Company were left leaning (OCD Region XII, March 7, 2002). The springs of the Dungan Lahek, Prisga and El Gawel were damaged (OCD Region XII, March 7, 2002).

 

14. T'boli, South Cotabato

In T'boli (pop.: 54,000), a cooperative building and a health center in Barangay Dumangas collapsed (OCD Region XII, March 7 and 11, 2002; Malaya and Philippine Daily Inquirer, March 7, 2001). A solar drier, barangay stage, day care building, roads of Barangay Afus, barangay properties, a bridge approach at Barangay Dumangas and two houses were damaged (OCD Region XII, March 7, 2002). About 90% of fishpens along Allah River and four houses were washed out (OCD Region XII, March 7 and 11, 2002). Landslides were observed at Barangays Afus and Sabang zigzag road (OCD Region XII, March 7, 2002). 3,898 families from the barangays of New Dumangas,, Laconon, Datal Dlanag, Salacafe and Tudok were isolated when the Sapali/Gao Bridge was washed out by the floodwaters of Lake Maughan (OCD Region XII, March 6 and 9, 2002).

 

15. Lake Maughan, Parker Volcano

Parker Volcano, one of the Philippine's 22 active volcanoes, has crater lake perched on its summit. The lake earlier breached in 1995 and repeat of this incident has been a serious concern for communities along the slopes of the volcano. After the earthquake, numerous landslides occurred at the crater wall near the Lake Maughan outlet. It covered two sabo dam areas. One of the landslides occurred at 3:20 AM coincident with a M5.0 aftershock (see list of aftershocks in this report; OCD Region XII, March 7, 2002). Water level at Gao reportedly increased after the earthquake. Brown smoke with accompanying sulfuric smell was observed at Mt. Melengbingay. Big cracks along trail Salacafe to Lake Maughan and from Salacafe to Barangay New Dumangas (OCD Region XII, March 7, 2002) were observed. The road from Sitio Montil to Barangay Salacafe proper upslope to Lake Maughan is unpassable. In the morning of March 7, 2002 at 5:20 AM, the walls of Lake Maughan collapsed and released waters that swept the town of New Dumangas, T'boli, South Cotabato and killed 3 people (Philippine Daily Inquirer, March 7, 2002 quoting a Major Julieto Ando of the Army's 6th Infantry Division in Mindanao).

 

16.Lake Sebu, South Cotabato

Three persons from Barangays Lamhalak and Lamdalag died when hollow blocks fell on them (OCD Region XII, March 7 and 9, 2002; Malaya and Philippine Star, March 7, 2002). Two were also injured (OCD Region XII, March 7, 2002). Two houses collapsed (OCD Region XII, March 7, 2002) and 285 houses were partially damaged (OCD, March 11, 2002) The town hall cracked (Manila Bulletin, March 7, 2002). A health center, 15 houses in Barangays Poblacion, Kubli and Lake Lahit and 20 school buildings in Barangay Lake Lahit were partially damaged (OCD Region XII, March 7, 2002). A two-hectare area planted to gemelina and lamcade was covered by landslide (OCD Region XII, March 7 and 11, 2002). A total of 116 families from Barangay Lamcade, Sitio Bagong Silang, Sitio Kaunlaran and Barangays Maculan and Halilan were evacuated (OCD Region XII, March 7, 2002) while 1247 families from Baranagays Halilan, Lower Maculan, Upper Maculam, Denlag and Lamcade were isolated (PDCC, March 10, 2002). Damage to Maculan Bridge costs 2 million pesos (PDCC, March 10, 2002).

 

17.Santo Nino, South Cotabato

The concrete fences of an elementary school in Baarangay Elementary School and the Barangay Teresita quadrangle collapsed (OCD Region XII, March 11, 2002). The old building of the publicc market also collapsed (OCD Region XII, March 11, 2002). A house in Barangay San Vicente was partially damaged (OCD Region XII, March 11, 2020). The terminal building and restaurants in Pob Public Market was damaged (OCD Region XII, March 11, 2002). A footbridge connecting Bagumbayan, Sultan Kudarat was damaged by floods amounting to six million pesos. Crops that were about to be harvested amounting to more than seven million pesos were destroyed by the flashfloods (PDCC, March 10, 2002).

 

18.Tupi, South Cotabato

Eight houses at Barangays Tuben and Bunao were partially damaged (OCD Region XII, March 7 and 11, 2002). Two old churches collapsed (OCD Region XII, March 7, 2002; Malaya and Philippine Daily Inquirer, March 7, 2002) while four others (SDA, Southern Baptist, Calvarym Tuben and Bunao) were damaged (OCD Region XII, March 7 and 11, 2002). A 30-m wall of the Old Knights of Columbus Building collapsed while a street light was damaged (OCD Region XII, March 7 and 11, 2002). One street light was damaged (OCD, March 11, 2002).

 

19.Tantangan, South Cotabato

Four houses were damaged while an old elementary school building at Barangay Libas collapsed (OCD, March 11, 2002). The walls and floors of the New Lambunao Elementary School and the multipurpose pavement and stage in Barangays New Lambunao and Cabuling cracked (OCD, March 11, 2002). The water system was also damaged (OCD, March 11, 2002). Two people were injured and were hospitalized (OCD Region XII, March 9, 2002).

 

20.Banga, South Cotabato

Nine houses were partially damaged while three houses were totally damaged (OCD region XII, March 11, 2002). A span of the Rizal Elementary School collapsed while the altar of a Catholic Church in Barangay Kusan was partially damaged (OCD region XII, March 11, 2002). The Sapali Bridge cracked (OCD Region XII, March 11, 2002). A piggery farm at Barangay Liwanany was partially damaged (OCD Region XII, March 11, 2002). Eight barangays were affected including livestock (OCD Region XII, March 11, 2002). Two people from Barangay Cinco were injured (OCD Region XII, March 9, 2002).

 

21.Norala, South Cotabato

Fourteen houses, two warehouses, a stage, a road, a motorcyle and the San Jose Elementary School Building were partially damaged (OCD, March 11, 2002).

 

22.General Santos City

General Santos City (pop:327,000) is the prime city of South Cotabato. A house totally collapsed (OCD-Region XII, March 7 and 11, 2002). Walls of schools (MSU HS, J.P. Laurel and Divina Gracia Elem. School), hotel near the coast (Sydney Hotel), and that of the Philippine National Police Headquarters fell. The editing machine of ABS-CBN media station and a steel water tank servicing 1000 people of a subdivision (Dona Soledad Subd) also fell. Two police cars were crushed when the walls of the PNP headquarters fell on them. Cracks were sustained by the walls of the Notre Dame of Dadiangas College, Yap Mabuhay Building and stockyard, SAFI Building, Dolores Hospital, SMC Stockyard, Kimball Plaza and Department Store, City Christian Fellowship Center, 10 & 10 24-Hour Grocery Store, New Era University, City Hall Hotel Filipino Building, Gaisano Mall, Peninsula Rural Bank, Gillamac Building, WHC Building., District Building, Barrio 8 Hall Building, Lamco Building, firewall of the Cooperative Building, a building under construction and the approach of Palian Bridge (OCD-Region XII, March 7, 2002). The approach of a bridge in Barangay General Paulino Santos was damaged (Philippine Daily Inquirer, March 7, 2002). There was panic at a tuna factory causing injury to 100 people among the 1,000 workers (Malaya, March 7, 2002). Four electric posts in Barangay Bula fell causing power failure (OCD-Region XII, March 7, 2002). Water supply was also disrupted during the earthquake. Power resumed after lunchtime on the same day. One 54-year old died of heart attack during the earthquake while nine others were injured (OCD-Region XII, March 7 and 9, 2002).

 

23. Cotabato City

Nine houses made of light materials at Barangay Kalanganan Mother collapsed (OCD Region XII, March 7 and 11, 2002). Two mosques were partially damaged Almonte Ext. and in Sitio Macaquiling, Barangay Sultan Kudarat. The Mega Market (OCD Region XII, March 7, 2002) suffered cracks . Power went off during the earthquake (Malaya, March 7, 2002). A man repairing a transmission line along Jose Lim Sr St. was electrocuted (OCD Region XII, March 7, 2002) Philippine Star, March 7, 2002). Two were injured by stray bullets which came from shots fired to rouse sleeping residents (OCD Region XII, March 7, 2002). Ten familiesin Barangay Kalanganan 2 were evacuated for fear of tsunami (OCD Region XII, March 7, 2002).

 

24. Zamboanga City

Animals were frightened causing dogs to howl and chickens to crow. Plates and bottles rattled waking up sleeping people. People described the quake as strong and caused dizziness and fear. Fright caused them to hide under tables
(Malaya, March 7, 2002)

 

25. Davao City

A person died of heart attack during the earthquake. Guests in high-rise hotels panicked and were hesitant in going back to their rooms for fear of aftershocks (Philippine Star, March 7, 2002). Power went off during the earthquake (Malaya, March 7, 2002).

 

26. Iligan City

An electric transformer in the commercial district fell (Philippine Star, March 7, 2002).

 

27. Other Places

Kidapawan City                          : Intensity IV
Bislig, Surigao del Sur               : Intensity III
Pagadian City                             : Intensity III
Mati, Davao Oriental                  : Intensity III
Dipolog City                                : Intensity III
Malaybalay, Bukidnon               : Intensity III
                                                        Power tripped off for some seconds after the quake
Butuan City                                 : Intensity II
Hibok Hibok Volcano                : Intensity I

 

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division

Aftershocks:

 

From March 6 to 9, parameters of 20 aftershocks were large enough to have been determined using the PHIVOLCS national seismic network and the USGS global network. Table 1 lists the parameters of these aftershocks while Figure 9 shows the plot of the locations of these events. The largest aftershock occurred at 2:27 AM on March 9. It was located south of the main shock, with depth of 5 km and Ms of 6.0. It was felt at Intensity III at General Santos City, Intensity II at Davao City and Intensity I at Cagayan de Oro City. Its mechanism as determined by USGS is normal faulting.

Fig 9. Aftershocks till March 9, 2002 as determined using PHIVOLCS and USGS data

 

 Date Local Time Depth Ms mb Mw  Epicenter  Intensity
 March 6  05:39 AM  33 5.0      6.240 ; 124.100   General Santos – Intensity III
March 6 11:25 AM 33   4.6   5.390 ; 126.940  
March 6 12:08 PM 33   4.5   6.160 ; 125.310 Kiamba – Intensity IV
March 6 01:10 PM 33       6.230 ; 124.320  
March 6 01:38 PM 33 4.7     6.230 ; 124.320  
March 6 10:36 PM 26 4.6 5.1   5.830 ; 124.79 0 General Santos City – Intensity III; Zamboanga City – Intensity II
March 7 03:19 AM 33 5.0     5.170 ; 124.720 Caused another landslide at Lake Maughan in Parker Volcano
March 7 11:30 AM 29 3.8     6.184 ; 124.657  
March 7 11:49 AM 12 3.3     5.557 ; 124.392  
March 7 06:37 PM 58 3.8   4.6 5.459 ; 124.306 General Santos – Intensity I
March 7 06:42 PM 10 3.4     6.026 ; 123.871  
March 7 09:56 PM 48 3.5     5.475 ; 124.373  
March 8 01:48 PM 32 3.3     5.592 ; 124.018  
March 8 03:56 AM 20 3.0     5.329 ; 124.501  
March 8 07:59 AM 24     4.9    
March 8 08:07 AM 23 2.9   4.9 5.269 ; 124.674 General Santos – Intensity I
March 8 08:37 AM 25     4.7 5.700 ; 124.420  
March 9 02:27 AM 23     6.0   General Santos – Intensity III; Davao – Intensity II; Cagayan de Oro – Intensity I
March 9 03:08 AM 1 3.2     5.209 ; 123.184 General Santos – Intensity II
March 9 03:35 AM 17 3.5     5.288 ; 123.782 General Santos – Intensity I

PHIVOLCS, 2002

Seismological Observation and Earthquake Prediction Division

PHIVOLCS Response:

 

A few hours after the earthquake, PHIVOLCS sent a letter informing Her Excellency President Gloria Macapagal Arroyo about the details of the event. Copies were also furnished the National Disaster Coordinating Council (NDCC) and the Department of Science and Technology. PHIVOLCS also deployed technical personnel from its General Santos City seismic station to investigate the impacts of the earthquake especially to the coastal towns fronting the location of epicenter. The PHIVOLCS staff reached as far as Kiamba but was advised by local authorities to desist from going further to Palimbang due to peace and order problems. PHIVOLCS seismic stations in General Santos City, Zamboanga, Davao and Cotabato were swamped with calls and inquiries from the local public and media. At the same time, they had to attend to the picking earthquake phase readings for sending to Main Office for processing. PHIVOLCS Main Office personnel took turns answering queries from the public especially 24 hours after the main shock. PHIVOLCS also issued several earthquake bulletins as more data came, the latest was bulletin no. 5. At the request of the NDCC, PHIVOLCS also issued an advisory to the coastal towns of Sarangani and Sultan Kudarat permitting them the local residents to go back to their homes. PHIVOLCS further advised them to seek the opinion of structural engineers regarding safety of their homes and places of work from future earthquakes.

 

click for a higher resolution

Fig 10. Copy of the PHIVOLCS advisory issued in the afternoon of March 7, 2002 to the National Disaster Coordinating Council (NDCC) as requested.

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division

References:

 

  • Bautista, Bartolome. 1996. Seismotectonic Implications of Recent Philippine Earthquakes. M.A. Thesis. State University of New York. Binghamton, New York.
  • Gutenberg
  • Fukushima and Tanaka (1990)
  • Malaya. March 7, 2002
  • Manila Bulletin. March 7, 2002
  • Office of Civil Defense (OCD). March 9, 2002. Update on the Effects of the Earthquake in Mindanao as of 8:00 AM 09 March 2002. 2 pages
  • Office of Civil Defense (OCD) Region XII. March 7, 2002. Consolidated Report Re Effects of the March 6, 2002 Tectonic Earthquake in Region XII. 8 pages.
  • Office of Civil Defense (OCD) Region XII. March 11, 2002. Summary of Effects of March 6, 2002 Tectonic Earthquake in Region XII. 8 pages.
  • Philippine Daily Inquirer. March 7, 2002
  • Philippine Star. March 7, 2002
  • PHIVOLCS Quick Response Team (QRT) report of the Investigation at Sarangani Province. March 7, 2002.
  • Provincial Disaster Coordinating Council (PDCC). March 11, 2002. Status Report as of March 10, 2002, 3:00 PM pn the Extent of Damage Caused by Earthquake that Struck South Cotabato on March 6, 2002, 5:15 AM. 3 pages
  • Tanioka, Yuchiro. 2002. Maps of tsunami models for the March 6, 2002 (Ms 6.8) Sarangani Earthquake. Unpubl. Data.

 

PHIVOLCS, 2002
Seismological Observation and Earthquake Prediction Division