ANSWER
The wavelength of the earthquake wave is 1000 m
EXPLANATION
From the question;
the speed,
[tex]c = 15 \: km {s}^{ - 1} = 15000 \: m {s}^{ - 1} [/tex]
frequency,
[tex]f = 15 \: Hz[/tex]
The relationship between wavelength,frequency and speed of a wave is given as
[tex]f = \frac{c}{ \lambda} [/tex]
This implies that,
[tex]{ \lambda} = \frac{c}{f} [/tex]
[tex]{ \lambda} = \frac{15000}{15} [/tex]
[tex]{ \lambda} = 1000 \: m[/tex]
Hence the wavelength of the earthquake wave is
[tex]1000 \: m[/tex]
