• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2005.03a
• /
• pp.11-17
• /
• 2005

Along the Ulsan Fault System, many Quaternary faults have been reported and investigated with outcrop observation and trench excavation to clarify the neotectonic movements and fault parameters such as length, displacement, slip rate and recurrence interval. In the northern part of the Ulsan fault system, we have interpreted small scale(1:10,000) aerial photographs and extracted lineaments by geomophological features to select trench site. After precise field survey and tracing for lineaments, two trench sites at Galgokri, Gyeongju were selected on the lineament to elucidate the fault movement history. One is successful in finding faults but the other is not. In the Galgok-Chisil trench(3m(w) x 1.5m(d) x 10m(l)), very closed two Quaternary faults cut the alluvial deposits of which age shows about 10-3ka. More than three times of fault movements can be inferred by geologic structures and C-14 dating. Repeatedly fault movements had been occurred before 10 ka, between 10ka-4.9 ka, between 4.9-1.4 ka at Galgok-Chisil trench section.

• Journal of the Korean Geophysical Society
• /
• v.3 no.4
• /
• pp.215-226
• /
• 2000

In order to map the acoustic basement and to locate fracture zones in the Galgok fault, seismic refraction data were acquired near the Chonbuk ranch in Gyeongju. Along three profiles of 72m(Line 1), 72m(Line 2), and 36m(Line 3) long, seismic signals were generated by a 5kg hammer. The refraction data were collected by employing twelve 8 Hz geophones at an interval of 3m and recording time of 192ms at a sampling rate of 0.2ms. The data are interpreted using GRM method. The top layer (Layer 1) is characterized as the velocity of approximately250 m/s and thickness of approximately 2.1m. This layer is regarded as a soil layer. Underneath Layer 1 lies unconsolidated layer (Layer 2) whose refraction velocity is determined to be $1,030{\sim}1,400m/s$. Layer 2 is approximately 4.6m thick and is regarded as a Quaternary gravel layer. The third layer (Layer 3) has the mean refraction velocity of $2,100{\sim}2,200m/s$ and is interpreted to be the acoustic basement. In some parts of Lines 1 and 3, the difference in depth to the top of Layer 2 is greater than 20 cm indicating the possibility of existence of Quaternary faults. Along Line 3 and the eastern part of Line 1, refracted energy from the acoustic basement was not recorded. This may highly indicate that a relatively large scale fault exists under the western part of Line 1.