Seismic microzonation and soil-structure resonance analysis in Suryabinayak Municipality, Bhaktapur, Nepal: insights from ambient vibration measurements

Figures & data

Figure 1. (a) Engineering geological map of Suryabinayak Municipality and surrounding areas with data acquisition points (redrawn and modified after Shrestha et al. (1998). Source: Department of Mines and Geology (DMG), Nepal. (b) Stratigraphic cross section profile of Bhaktapur district from South (S) to North (N). Redrawn and modified after Kawan et al. (2019)

Figure 2. (a) Instrumentation for the data acquisition; (b) comparison of frequency obtained from geophone and accelerometer.

Figure 3. Microtremor measurement station in 200 × 200 m and 400 × 400 m grid spacing and location of building considered. B = building.

Table 1. Guidelines recommended by SESAME (2004) for microtremor data acquisition.

Type of parameter	Main recommendations
Recording duration	Minimum expected f0 [Hz]	Recommended minimum recording duration [min]
	0.2	30′
	0.5	20′
	1	10′
	2	5′
	5	3′
	10	2′
Recording parameters	The sensor should be level, as recommended by the manufacturer.
	The gain level should be fixed at the maximum possible level without any signal saturation
In situ-soil sensor coupling	The sensor should be set down directly on the ground wherever possible.
	The sensor should not be set down on soft grounds or soil saturated after rain.
Artificial soil-sensor coupling	The plates should not be placed on soft materials such as foam rubber, cardboard, etc.
	The sensor should be installed in a sand pile or in a container filled with sand on steep slopes that do not allow correct sensor leveling.
Nearby structures	The recording should be avoided near structures such as buildings, trees, etc in case of wind blowing.
	Measurement should not be done above underground structures such as car parks, pipes, sewerage, drain lids, etc.
Weatheric conditions	Wind: The sensor should be protected from the wind (> 5 m/s approximately).
	Rain: Measurements should not be taken under heavy rain.
	Temperature: sensor and recorder should be checked in compliance with the manufacturer’s instructions.
	Meteorological perturbations: weather conditions should be noted on measurement field sheets.
Disturbances	Monochromatic sources: Data should not be taken near construction machines, industrial machines, pumps, generators, etc.
	Transients: The recording duration should be increased in case of transients (human walks, vehicle movement) for enough windows during analysis.

Figure 4. Typical velocity time history graph of measured data; (a) vertical direction (UD); (b) North-South (NS) direction; (c) East-West (EW) direction.

Figure 5. Representative picture for microtremor measurements of building ID (a) B9 and (b) B12; data acquisition of the building on (c) the top floor and (d) the bottom floor of the building (B12).

Figure 6. Representative Horizontal to Vertical Spectral Ratio (HVSR) graph of microtremor measurement stations. The black line represents the average H/V spectra graph; the dotted line represents the average H/V ± standard deviation

Figure 7. (a) Frequency-based microzonation map of the study area and resonance possibility of buildings with soil. B = building. (b) Stratigraphic features of Borehole BH1 and BH2. Source: modified after Kawan et al. (2019).

Figure 8. Frequency-based cross-sectional profile along (a) S1-N1 (transverse direction) and (b) W1-E1 (longitudinal direction) of the study area.

Figure 9. Floor Spectral Ratio (FSR) vs frequency (Hz) for B6; B9; B16 and B19.

Table 2. Soil-structure resonance possibility of all measured buildings.

Building ID	No. of story	Longitudinal frequency (Hz)	Transverse frequency (Hz)	Freefield frequency (Hz)	Level of danger
B1	4	2.98	3.76	1.89	Low
B2	3	4.53	3.76	3.27	High
B3	2	6.28	7.92	1.42	Low
B4	5	5.21	2.84	1.74	Low
B5	3	5.72	5.21	3.76	low
B6	5	4.13	2.84	2.6	High
B7	5	3.94	2.98	1.02	Low
B8	3	4.32	4.97	3.82	High
B9	2	7.22	6.57	2.72	Low
B10	2	9.11	8.69	9.09	High
B11	4	3.59	2.71	1.02	Low
B12	5	4.13	3.43	3.05	High
B13	4	4.53	3.12	1.11	Low
B14	4	3.59	3.27	2.84	Medium
B15	2	7.92	7.22	0.35	low
B16	3	4.53	4.53	4.74	High
B17	3	5.21	5.46	3.96	Low
B18	2	7.22	6.89	2.22	Low
B19	4	3.76	3.59	4.92	Medium
B20	5	4.32	2.36	4.93	High

Figure 10. Fundamental frequency and height relationship of surveyed building (a) along longitudinal direction; and (b) along transverse direction.

Figure 11. Soil-structure resonance possibility of Suryabinayak Municipality based on height of building.

Shrestha OM, Koirala A, Karmacharya SL, Pradhananga UB, Pradhan PM, Karmacharya R. 1998. Engineering and environmental geological map of the Kathmandu Valley, scale 1:50,000. Kathmandu: Department of Mines and Geology.

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SESAME. 2004. Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation. [place unknown]: European Commission -Research General Directorate.

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Data availability statement

The data underlying this article will be shared on the reasonable request to the corresponding author.