Landslides triggered by the 2015 M_w 6.0 Sabah (Malaysia) earthquake: inventory and ESI-07 intensity assignment

Abstract

Abstract. On 4 June 2015, a Mw 6.0 earthquake occurred in the Sabah region (Malaysia), triggering widespread landslides along the slopes of Mt. Kinabalu. Despite the moderate magnitude, the Sabah earthquake was very efficient in triggering landslides: here I provide an inventory containing 5198 slope movements, mapped in an 810 km2 wide area. I investigate earthquake intensity using the Environmental Seismic Intensity (ESI-07) scale, which is a macroseismic scale based exclusively on earthquake environmental effects. The epicentral ESI-07 intensity is assessed at IX, considering the dimension of the area affected by secondary effects; such figure agrees well with a dataset of global earthquakes. I estimate the volume of individual landslides using area–volume scaling laws; then, I assign an ESI-07 intensity to each mapped landslide. I document that the selection of a given area–volume relation has a minor influence on the ESI-07 assignment. Then, I compare ESI-07 values to landslide density and areal percentage on a 1 km2 grid; such parameters are widely adopted in the description of earthquake-triggered landslide inventories. I argue that their integration with the ESI-07 scale may provide an effective way to compare earthquake damage on a variety of spatial and temporal scales. The methodological workflow illustrated here is useful in joining the scientific communities dealing with the development of earthquake-triggered landslide inventories and with ESI-07 assignment; I believe this effort is beneficial for both communities.

Environmental effects following a seismic sequence: the 2019 Cotabato - Davao del Sur (Philippines) earthquakes

“…EQ1 has lower maximum values than the other earthquakes, regardless of the intensity scale being used. ESI-07 epicentral values are slightly higher than maximum MM values, in good agreement with what has been observed for other case studies (see Ferrario et al, 2022). CDI values peak for EQ2, which seems to contradict the results obtained by other scales; however, the 9.1 value may be an outlier, since the second-most high value is 8.5.…”

“…Open dots in Figure 7c include both the events analyzed by Keefer (1984) and more recent data; anyway, the Cotabato-Davao del Sur earthquakes lie below the upper boundary proposed by Keefer (1984). Figure 7d shows the comparison with other earthquakes analyzed using the ESI-07 scale (dataset after Ferrario et al, 2022); also in this case the earthquakes analyzed here are in agreement with previous data. All these studies testify that earthquakes can repeatedly trigger environmental effects at the same place; earthquake damage, and thus macroseismic intensity, can remain constant or increase during a seismic sequence, but it can never decrease.…”

“…Additionally, the epicentral ESI-07 intensity can be assigned based on the dimension of the area affected by secondary effects, or on the length of surface faulting. Most of the earthquakes analyzed using the ESI-07 scale follow this procedure (Ferrario et al, 2022).…”

“…The assessment of an ESI-07 value for a slope movement is based on the amount of mobilized volume (in m 3 ); we measure the area of each mapped landslide and we convert to volume using Equation ( 1), adopting the scaling law proposed by Larsen et al (2010). Recently, Ferrario (2022) investigated the epistemic uncertainty related to the choice of area-volume relations, showing that it does not heavily affect the obtained ESI-07 value, while a much higher influence is due to the quality and reliability of input data (i.e., landslide inventory).…”

“…18 Earthquake 4 (g-h); left-hand panels show PEIS isoseismals (after Perez et al, 2019Perez et al, , 2020 In Figure 7, we compare the Cotabato -Davao del Sur events with other earthquakes on a global scale (modified after Ferrario, 2022). Figure 7a shows the number of landslides with respect to moment magnitude, while Figure 7b shows the total landslide area (sum of individual landslides); the lines represent the scaling relation proposed by Malamud et al (2004).…”