Offset Channels May Not Accurately Record Strike‐Slip Fault Displacement: Evidence From Landscape Evolution Models

Abstract

Slip distribution, slip rate, and slip per event for strike‐slip faults are commonly determined by correlating offset stream channels—under the assumption that they record seismic slip—but offset channels are formed by the interplay of tectonic and geomorphic processes. To constrain offset channel development under known tectonic and geomorphic conditions, we use numerical landscape evolution simulations along a theoretical strike‐slip fault with uniform and steady uplift, erosion, and diffusion. We investigate the influence of four tectonic parameters (fault zone width, earthquake recurrence interval, variance of the recurrence interval, and total slip relative to channel spacing) on offset channel development through multiple earthquake cycles. Analysis of >3,000 automatically measured offsets from >135 simulations suggests ~30% variability in individual measurements, but modeled displacement is recovered by averaging multiple measurements. However, the average of multiple offset measurements systematically underestimates modeled slip except when the fault zone is less than ~5 m wide, total slip is less than channel spacing, and offsets are measured shortly after an earthquake. In these simulations, postearthquake landscape evolution widens the geomorphic expression of the fault zone and modifies apparent channel offsets. We distinguish this “geomorphic fault zone” from the tectonic fault zone (zone of coseismic distributed deformation). This study highlights the capability of landscape evolution models to explore a range of conditions not easily defined in natural examples and the importance of averaging multiple measurements. Our results verify that paleoseismic studies must consider how geomorphic change has modified offset markers and use caution interpreting slip histories with multiple earthquakes.

Assessment of tectonic control on the development of low mountains moderate relief in the Outer Carpathians (Southern Poland)

“…The other offset channel in the eastern part of the study area, within the Łękawka catchment, on the southern slopes of the Beskid Mały Mts., shows potential sublatitudinal dextral strike-slip faults disturbing rivers flowing to the south ( Figure 13C). Observed river deflections vary from < 50 m to > 300 m, which might implicate several stages of fault activity (e.g., Reitman et al 2019). In the eastern part, the proposed structure follows the trace of a previously detected fault ( Figure 13C).…”

“…We found a few examples of offset channels in the Soła River catchment (Figure 13) that in the areas of high tectonic activity are usually interpreted as the evidence of strike-slip fault displacements (e.g., Gaidziket al 2016;Reitman et al 2019). Presented examples do not coincide with the variations in lithology, but in most of the cases, these also do not follow the recorded fault network.…”

Strain and Velocity Across the Great Basin Derived From 15‐ka Fault Slip Rates: Implications for Continuous Deformation and Seismic Hazard in the Walker Lane, California‐Nevada, USA

“…Major earthquakes in eastern Asia commonly include deformation spanning regions tens of kilometers in width along faults zones 100 km or more in length, like the 1889 Chilik earthquake in Kyrgyzstan (Abdrakhmatov et al., 2016), the 1905 Bulnay earthquakes in northern Mongolia (e.g., Baljinnyam et al., 1993; Choi et al., 2018), and the 1957 Gobi‐Altay earthquake (Florensov & Solonenko, 1963; Kurushin et al., 1997). Furthermore, numerical models of landscape evolution suggest that strike‐slip offsets in wide fault zones underestimate modeled slip, as do offsets measured many years after an earthquake (Reitman et al., 2019).…”

“…Furthermore, numerical models of landscape evolution suggest that strike-slip offsets in wide fault zones underestimate modeled slip, as do offsets measured many years after an earthquake (Reitman et al, 2019).…”

Slip and Strain Accumulation Along the Sadie Creek Fault, Olympic Peninsula, Washington

“…For example, Channels B, C, and D are located on the same hillslope, within ∼100 m of each other ( Figure 4a), and show preferred offsets of 15.6, 6.5, and 26.0 m, respectively (Table 1). We are confident that these closely spaced channels (and others along the NOFZ) preserve an accurate record of cumulative fault slip because they are spaced farther apart than the total amount of offset, the variance between measurements is >30% of the preferred offset value, we used multiple geomorphic markers to calculate each offset value, and we carefully considered the interseismic geomorphic modification during the measuring processes (see Section 4 and supporting information S3 and S4; Reitman et al, 2019). Therefore, strike-slip displacement may correlate better with channel incision age than the deposit age dated through detrital charcoal.…”