Fatima Marjan Keshia Satriani, Titi Anggono, Mia Uswatun Hasanah

Karakteristik Atenuasi Gelombang Seismik di Daerah Ternate, Maluku Utara dengan menggunakan Analisis Gelombang Coda

Introduction

Karakteristik atenuasi gelombang seismik di daerah ternate, maluku utara dengan menggunakan analisis gelombang coda. Penelitian ini mengukur atenuasi gelombang seismik di Ternate, Maluku Utara menggunakan analisis gelombang coda. Menunjukkan aktivitas tektonik kuat dengan nilai Q0 & Qc rendah.

Abstract

The convergence of the Philippine Plate, the Eurasian Plate, the Australian Plate, and the double subduction between the Molucca Sea Plate, the Sangihe Through, and the Halmahera Through have created a complex tectonic setting in North Maluku. Due to intense tectonic activity, this region frequently experiences the possibility of tectonic events like earthquakes. In the attenuation seismology approach, seismic waves propagating below the surface are measured for amplitude amplification and attenuation. Seismic wave attenuation propagating in this region is described using the coda attenuation method on coda seismic waves. In order to determine the degree of tectonic activity in the Ternate region, 129 earthquake data points from four sites in North Maluku that were less than 40 kilometers deep were processed. Stations SP01 and SP02 are situated on Ternate Island, whereas stations BB06 and SP28 are situated on Hiri Island. A sampling frequency of 2 – 10 Hz and a window length of 20 – 120 s were used to get values of the coda (Q0), η, Qc, and attenuation (Qc-1). Twi times the S-wave’s arrival time is assumed for the coda wave. The coda variation values (Q0) were recorded as follows: an average of 112. 167 for station SP01, 91.071 for station SP02, 116.089 for station SP28, and 112.843 for station BB06. The value increases and decreases within the 20 – 40 s range. The values of attenuation and (Q0) are inversely related. The Q0 and Qc values obtained are low due to the high damping value in the Ternate area. The high damping (Qc-1), high eta (η) value (>1), and low Q0 value (<200) are thought to be signs of strong tectonic activity in the Ternate, Halmahera, North Maluku region.

Review

The paper "Karakteristik Atenuasi Gelombang Seismik di Daerah Ternate, Maluku Utara dengan menggunakan Analisis Gelombang Coda" presents a timely and relevant investigation into seismic wave attenuation in the tectonically complex region of North Maluku. Leveraging 129 earthquake events recorded at four stations across Ternate and Hiri Islands, the authors apply the coda wave attenuation method to characterize the seismic environment. The study successfully quantifies crucial parameters such as Q0, η, and Qc-1, linking these directly to the intense tectonic activity prevalent in the area. The findings, particularly the consistently low Q0 and Qc values coupled with high damping, provide valuable insights into the crustal properties and stress conditions of a region prone to frequent and significant seismic events. The study's primary strength lies in its focus on a critical geophysical parameter—seismic wave attenuation—within a high-priority seismic hazard zone. The use of a well-established coda wave method and a reasonably robust dataset of 129 events from shallow earthquakes enhances the reliability of the results. The explicit connection drawn between the derived attenuation parameters (low Q0, high η, high damping) and strong tectonic activity is a significant contribution to understanding the region's geodynamics. However, the abstract could benefit from clarification on certain points. For instance, the statement that "The value [Q0] increases and decreases within the 20 – 40 s range" is vague and requires further elaboration to understand what specific variation (e.g., spatial, temporal, or frequency-dependent) it refers to. A brief justification for the chosen sampling frequency (2-10 Hz) and window length (20-120 s) could also strengthen the methodological discussion. Additionally, assuming "Twi times" refers to "twice" the S-wave arrival time for the coda wave onset should be explicitly confirmed. In conclusion, this research offers an important contribution to the seismological understanding of the Ternate region, providing quantitative measures of seismic attenuation that underscore its highly active tectonic nature. The derived low Q0 and Qc values, indicative of significant energy loss, align well with expectations for a heavily fractured and stressed crust associated with complex plate interactions. For future iterations or a full manuscript, it would be beneficial to delve deeper into the spatial variations of attenuation parameters observed across the four stations and discuss their potential correlation with specific local geological structures or fault systems. A more detailed analysis of the frequency dependence of Qc and Q0 could also provide further insights into the scattering and intrinsic absorption mechanisms at play. This would further enhance the impact and generalizability of these valuable findings, contributing significantly to regional seismic hazard assessment.

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