The analysis and mapping of an urban planning area in risk and hazard dimensions using earthquake-MASW-VES data: the case of Yenişehir (Bursa), Turkey

Abstract

The study area was defined by geophysical level maps and earthquake parameters. Geophysical measurements were collected from the Mesudiye formation and alluvial units. The seismic Vs–Vp–Vs30, dynamic parameter and electrical resistivity values of the layers were calculated. Vs–Vp–Gmax–σ–Ak and ρ level maps were prepared for depths of 0–5, 5–10, and > 10 m. Seismic Vs30 and groundwater maps were prepared for risk/hazard and liquefaction interpretations, and a risk map was drawn from Ak–Vs30–groundwater maps. In the Mesudiye formation, the average ground amplification value is Ak = 2.21 and according to this value, the danger level is class A and low (Ansal et. all 2004). In alluviums, the average Ak was calculated as 2.51. According to this value, its class is B (medium) and the danger level is medium level. According to the level maps, it was observed that seismic velocities and electrical resistivities increased, and they were compatible with the geological units when passing to the more tight-ground Mesudiye formation from loose-porous-water-saturated alluvial units towards the north and deeper. It was determined that the alluvial grounds with low resistivity (8–30 Ohm m) are moderately corrosive–corrosive; groundwater levels are at ~ 5 m and contain different geological gradations. Therefore, the alluviums were interpreted as a risky area. This interpretation was also proved and supported with the results of the earthquake parameters. It was determined that as the magnitude of the earthquake increased, the probability of a larger earthquake occurred with a longer recurrence year. It was found that the frequency of recurrence of earthquakes with M ≤ 5.5 within 10–50–75–100 years was higher, and M ≥ 6 decreased. For M = 7.4, the average amax = 0.31 g was calculated, and it was determined the liquefaction risk is high hazard, especially in fine-gravel-sandy alluviums (in the south). Therefore, these areas may be more affected by the earthquake.