The SW4 output text does not indicate any errors, but I see many nan values ​​in the result file.

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The SW4 output text does not indicate any errors, but I see many nan values ​​in the result file. What is the reason?Below is my input text：
grid x=136000 y=86000 z=35000 h=500 lat=38.46371 lon=-122.161196 az=143.638 proj=tmerc ##Mw7.0
refinement zmax=15000
time t=90
attenuation minppw=6
rupture file=/sh3/ysuanbase/home/yeesuan14830/yeesuan/test/sub0.5Mw7.srf ##I used Song rupture generator to generate the SRF file, and the sub-fault size is 0.5km.
supergrid gp=31
gmg filename=USGS_SFCVM_v21-1_detailed.h5 directory=/sh3/ysuanbase/home/yeesuan14830/yeesuan/test/
globalmaterial vsmin=600