Step-response signals recorded during earthquakes in Alaska

Abstract

We present waveform record sections of 18 earthquakes recorded the Minto Flats fault zone in central Alaska. These include the largest earthquakes to have occurred within the Minto Flats fault zone since the installation of the 13-station FLATS network in September 2015 (Tape and West, 2014). Several seismograms from these earthquakes exhibit a ``step-response signal'' that is a long-period, unwanted signal that does not reflect regional ground motion. We use the term ``anomalously high amplitudes'' to refer to amplitudes within a certain bandpass that exceed the amplitude of earthquake ground motion (within the same bandpass). We attribute anomalously high amplitudes to three possibilities: (1) step-response signal due to local tilt or other effect, (2) step-response signal due to defective sensor, (3) digitizer clipping, (4) high noise (especially before the earthquake). We find widespread occurrences of the step-response signal for earthquakes in the Minto Flats fault zone.