It is commonly assumed that ground-based gravitational wave ( GW ) instruments will not be sensitive to supermassive black holes ( SMBHs ) because the characteristic GW frequencies are far below the \sim 10 - 1000 Hz sensitivity bands of terrestrial detectors .
Here , however , we explore the possibility of SMBH gravitational waves to leak to higher frequencies .
In particular , if the high frequency spectral tail asymptotes to \tilde { h } ( f ) \propto f ^ { - \alpha } , where \alpha \leq 2 , then the spectral amplitude is a constant or increasing function of the mass M at a fixed frequency f \gg c ^ { 3 } / GM .
This will happen if the time domain waveform or its derivative exhibits a discontinuity .
Ground based instruments could search for these universal spectral tails to detect or rule out such features irrespective of their origin .
We identify the following processes which may generate high frequency signals : ( i ) gravitational bremsstrahlung of ultrarelativistic objects in the vicinity of a SMBH , ( ii ) ringdown modes excited by an external process that has a high frequency component or terminates abruptly , ( iii ) gravitational lensing echos and diffraction .
We estimate the order of magnitude of the detection signal to noise ratio for each mechanism ( i , ii , and iii ) as a function of the waveform parameters .
In particular for ( iii ) , SMBHs produce GW echos of inspiraling stellar mass binaries in galactic nuclei with a delay of a few minutes to hours .
The lensed primary signal and GW echo are both amplified if the binary is within a \sim 10 { deg } ( r / 100 M ) ^ { -1 / 2 } cone behind the SMBH relative to the line of sight at distance r from the SMBH .
For the rest of the binaries near SMBHs , the amplitude of the GW echo is \sim 0.1 ( r / 100 M ) ^ { -1 } of the primary signal on average .