Laboratory Observations of Tremor‐Like Events Generated During Preslip

Abstract

The origins of tremors and their relation to fault slip and impending earthquakes remain unclear. Laboratory studies on tremor‐like acoustic emission events generated during preslip may shed some light on the above issues. We conducted stick‐slip experiments and observed tremor‐like events and preslip in the laboratory. The results show the following. (1) The dominant frequency of tremor‐like events increases with accelerating preslip. (2) The evolution of tremor‐like events is spatiotemporally consistent with that of preslip. (3) Interactions between preslip and high‐frequency events indicate the formation of a positive feedback effect between the expansion of preslip and failure of asperities, which leads to stick‐slip instability. Thus, we propose that tremors may be caused by stress variations derived from asperity interactions along fault surfaces at dry conditions. The increasing dominant frequency of tremors may imply the accelerating preslip of an upcoming earthquake.

Laboratory Observations of Repeated Interactions between Ruptures and the Fault Bend Prior to the Overall Stick-Slip Instability Based on a Digital Image Correlation Method

“…Namely, the rupture initiated in one fault segment was hindered by the fault bend and accelerated before and after it propagated across the fault bend to another segment, respectively, as shown in Figure 4a,b, Figure 5a-c, and Figure 6a,b. This effect indicates the interaction between the fault bend and the rupture, which is similar to the effect that the asperities hinder and promote the rupture before and after the failure of the asperities in straight faults, respectively [25,35]. On the other hand, unlike straight faults where the failed asperities have been deformed and do not interact with the rupture in the same seismogenic process [25,35], a fault bend is a geometric structure of the fault and is accordingly difficult to be deformed by the rupture.…”

“…This effect indicates the interaction between the fault bend and the rupture, which is similar to the effect that the asperities hinder and promote the rupture before and after the failure of the asperities in straight faults, respectively [25,35]. On the other hand, unlike straight faults where the failed asperities have been deformed and do not interact with the rupture in the same seismogenic process [25,35], a fault bend is a geometric structure of the fault and is accordingly difficult to be deformed by the rupture. As a result, the fault bend can interact with the rupture in multiple cycles during the same seismogenic process, which was observed in the alternative propagation stage in our experiment.…”

“…Each stress drop in Figure 2 corresponds to a stick-slip instability event of the fault. See our previous paper [25] for details on the loading system.…”

“…Each stress drop in Figure 2 corresponds to a stick-slip instability event of the fault. See our previous paper [25] for details on the loading system. The illustration on the right is an enlarged view of the fault slip gages in the dashed circle around the fault bend.…”

“…For instance, only dozens of strain gages can be used to cover a fault of tens of centimeters long, which were usually used in previous experimental studies [18,19,[21][22][23][24]. However, via the digital image correlation (DIC) method, thousands of pixels can be used by camera photography to observe the slip and deformation along a fault of equivalent length [25][26][27][28][29][30]. Therefore, compared with the contact type observation, the spatial sampling rate of the DIC method is dramatically higher.…”