Seismic microzonation maps of Phrae city, Northern Thailand

Figures & data

Figure 1. Geological map of the study area, the MASW test sites (numbered red dots) and locations of the boreholes (numbered blue dots) used in the study.

Figure 2. Active faults in Northern Thailand (Thitimakorn 2013).

Table 1. The NEHRP soil profile type classification for seismic amplification (BSSC 2003).

NEHRP soil type	General description	Average Vs(30) (m/s)
A	Hard rock	>1500
B	Rock	760 < Vs ≤ 1500
C	Very dense soil and soft rock	360 < Vs ≤ 760
D	Stiff soil 15 ≤ N ≤ 50 or 50 kPa ≤ Su ≤ 100 kPa	180 ≤ Vs ≤ 360
E	Soil or any profile with more than 3 m of soft clay defined as soil with PI > 20, w ≥ 40% and Su < 25 kPa.	≤180
F	Soils requiring site-specific evaluations

Note: N: SPT blow count, Su: Undrained shear strength, PI: Plasticity index, w: water content.

Figure 3. Schematic diagram showing the MASW data acquisition field setup.

Figure 4. Processing steps for MASW data showing the (a) MASW shot gather, (b) corresponding overtone image with picked fundamental-mode of dispersion curve, and (c) Vs profile.

Figure 5. Variation of Vs with depth in (a) alluvium (Qa) and (b) terrace (Qt) soil units.

Figure 6. Representative soil profile in the study area from the six boreholes.

Figure 7. Plot of Vs₍₃₀₎ in the (a) alluvium (Qa) and (b) terrace (Qt) soil units at different MASW stations.

Figure 8. Map showing the Vs₍₃₀₎ around Phrae City and its location within Thailand.

Table 2. NEHRP site classification for each soil unit.

Site no.	Latitude	Longitude	Soil type	Vs(30), m/s	NEHRP class	Amplification*	Site period**
1	616729	2003012	Qt	284	D	2.29	0.42
2	618852	2002641	Qa	352	D	2.02	0.34
3	621161	2003133	Qa	355	D	2.01	0.34
4	623389	2003067	Qa	285	D	2.29	0.42
5	624645	2002647	Qt	368	C	1.96	0.33
6	626935	2002950	Qt	401	C	1.86	0.30
7	627453	2005356	Qt	365	C	1.97	0.33
8	624840	2005278	Qt	362	C	1.98	0.33
9	623685	2004788	Qa	372	C	1.95	0.32
10	620300	2004606	Qa	273	D	2.35	0.44
11	618217	2004609	Qa	318	D	2.14	0.38
12	617486	2005397	Qa	299	D	2.22	0.40
13	617370	2006579	Qt	269	D	2.37	0.45
14	619257	2007308	Qa	317	D	2.15	0.38
15	621836	2006569	Qa	281	D	2.31	0.43
16	623831	2006975	Qa	308	D	2.18	0.39
17	625139	2007459	Qa	358	D	2.00	0.34
18	627283	2007595	Qt	369	C	1.96	0.33
19	626902	2008486	Qt	373	C	1.95	0.32
20	625135	2009624	Qa	348	D	2.03	0.34
21	623865	2008475	Qa	336	D	2.07	0.36
22	622039	2010078	Qa	356	D	2.00	0.34
23	619457	2009031	Qa	328	D	2.10	0.37
24	617717	2008446	Qa	304	D	2.20	0.39
25	618657	2011031	Qa	301	D	2.21	0.40
26	619756	2010620	Qa	300	D	2.22	0.40
27	621827	2010643	Qa	308	D	2.18	0.39
28	623479	2010633	Qa	283	D	2.30	0.42
29	625702	2011094	Qa	275	D	2.34	0.44
30	627098	2011073	Qa	401	C	1.86	0.30
31	625805	2010408	Qa	335	D	2.08	0.36
32	627198	2012310	Qt	428	C	1.79	0.28
33	627905	2008923	Qt	395	C	1.88	0.30
34	627485	2006305	Qt	412	C	1.83	0.29
35	627580	2002594	Qt	434	C	1.78	0.28
36	621645	2007735	Qa	256	D	2.44	0.47
37	622351	2005117	Qa	268	D	2.37	0.45
38	622084	2003687	Qa	283	D	2.30	0.42
39	623057	2010273	Qa	290	D	2.27	0.41
40	620366	2013066	Qt	315	D	2.16	0.38

Note: Qa = Alluvium deposit. Qt = Terrace deposit. *Midorikawa (1987). **Di Julio (2001).

Figure 9. Map of NEHRP site classifications for Phrae City.

Figure 10. Preliminary soil amplification map of Phrae city.

Figure 11. Natural site period map of Phrae City.

Table 3. Natural period of buildings with different stories.

Number of stories	Natural period of the building (T)
1	0.1
2	0.2
3–4	0.3–0.4
5–6	0.5–0.6
10	1.0

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