Sains Malaysiana 30: 1-11 (2001)                                                                                                     Sains Bumi /

Earth Sciences 

Application of Seismic Gun for a Seismic Refraction

Investigation of a Peat Basin at Gedong, Serian, Sarawak

Umar Hamzah & Abdul Rahim Samsudin

Program Geologi

Pusat Pengajian Sains Sekitaran dan  Sumber Alam

Fakulti Sains dan Teknologi

Universiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor D.E. Malaysia

ABSTRAK

Satu survei seismos biasan telah di lakukan di kawasan Gedong yang terletak di sekitar 20 kilometer dari bandar Serian, Sarawak untuk menyiasat ketebalan tanah gambut dalam lembangan seluas beberapa kilometer persegi. Dalam survei ini, rentasan dibuat pada dua garis memotong pada arah utara selatan dan timur-barat lembangan dengan sela stesen pengukuran pada jarak beberapa kilometer di antara setiap satu. Data di perolehi dengan teknik resiprokal di mana tenaga dilepaskan di sepanjang rebakan pengesan atau geofon menggunakan letupan peluru senapang seismos (Buffalo gun) yang larasnya di benamkan sedalam di sekitar 0.6 meter ke dalam tanah gambut berair atau lembab. Tenaga yang biasanya diperolehi melalui ketukan tukul ke atas keping besi tidak dapat dihasilkan di kawasan ini kerana bahan permukaannya lembut dan berair. Data diproses dengan perisian komputer REFRACT dan profil-profil kedalaman-halaju diperolehi di setiap stesen pembacaan. Berdasarkan halaju gelombang P yang diukur dan maklumat penggerudian auger cetek, lapisan pertama yang berketebalan di sekitar 0.4 hingga 11.4 m dengan purata 4.4 m adalah ditafsirkan sebagai gambut tepu air berjulat halaju di antara 274 hingga 590 m/s dengan purata 419 m/s. Lapisan kedua ialah lempung tepu air berketebalan di antara 2.6 hingga 39.1 m dengan purata 15.7 m. Halaju lapisan ini ialah di antara 1193 hingga 2074 m/s dengan purata 1515 m/s. Lapisan ketiga yang dicerap dalam survei ini merupakan batu dasar yang terdiri daripada batuan volkanik Serian yang kelihatan tersingkap di sekitar kawasan kajian. Halaju lapisan ini ialah daripada 3144 hingga 8113 m/s dengan halaju purata di sekitar 5288 m/s.

ABSTRACT

A seismic refraction survey has been carried out on an area in Gedong situated about several kilometres from Serian town, Sarawak in order to investigate the thickness of peat in a basin of a few kilometres square in area. For this survey data is acquired along two traverse lines across north-south and east-west of the basin with each station is at several kilometres in interval. The reciprocal technique is used in data acquisition employing bullet explosion seismic gun (buffalo gun) as the source of energy. Shots are fired at fixed distances along the geophones or sensors spread at depth of approximately 0.6m in the wet and saturated peat soil. Source energy normally obtained by hammering on a steel plate is not suitable in this soft and watery top material condition. Computer software REFRACT is used in data processing and the resulting depth-velocity profile together with the P­-wave velocity and shallow augering informations are used in the interpretation of the seismic profile for each station. The first layer is interpreted as water saturated peat of thicknesses ranging from 0.4 to 11.4m with an average of 4.4m. Its velocity ranges from 274 to 590 m/s with an average of 419 m/s. The second layer consists of saturated clay with thicknesses ranging from 2.6 to 39.1 m and 15.7 m in average. This layer velocity ranges from 1193 to 2074 m/s with an average of 1515 m/s. The third layer is interpreted as bedrock with velocities ranging from 3144 to 8113 m/s giving an average of approximately 5288 m/s.

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