Volcanic activity at the Santiaguito dome complex (Guatemala) is characterized by lava extrusion interspersed with small, regular, gas-and-ash explosions that are believed to result from shallow magma fragmentation; yet, their triggering mechanisms remain debated. Given that the understanding of source processes at volcanoes is essential to risk assessments of future eruptions, this study seeks to shed light on those processes. We use data from a permanent seismic and infrasound network at Santiaguito volcano, Guatemala, established in 2018 and additional temporary stations, including a seismic array deployed during a 13-day field investigation in January 2019 to analyze and resolve the source characteristics of fragmentation leading to gas-and-ash explosions. Seismic data gathered within a distance of 4.5 km from the vent show a weak seismic signal 2–6 s prior to the explosions and associated main seismic signal. To resolve the source location and origin of the seismic signals, we first used ambient noise analysis to assess seismic velocities in the subsurface and then used two-dimensional spectral element modeling (SPECFEM2D) to simulate seismic waveforms. The analyzed data revealed a two-layer structure beneath the array, with a shallow, low-velocity layer (v_s = 650 m/s) above deeper, high-velocity rocks (v_s = 2,650 m/s). Using this velocity structure, possible source mechanisms and depths were constrained using array and particle motion analyses. The comparison of simulated and observed seismic data indicated that the precursory signal is associated with particle motion in the RZ-plane, pointing toward the opening of tensile cracks at a depth of ∼600 m below the summit; in contrast, the main signal is accompanied by a vertical single force, originating at a shallow depth of about ∼200 m. This suggests that the volcanic explosions at Santiaguito are following a bottom-up process in which tensile fractures develop at depth and enable rapid gas rise which leads to the subsequent explosion. The result indicates that explosions at Santiaguito do not occur from a single source location, but from a series of processes possibly associated with magma rupture, gas channeling and accumulation, and fragmentation. Our study provides a good foundation for further investigations at Santiaguito and shows the value of comparing seismic observations with synthetic data calculated for complex media to investigate in detail the processes leading up to gas-ash-rich explosions found at various other volcanoes worldwide.

Santiaguito圆顶综合体（危地马拉）的火山活动的特征是熔岩挤压散布着小而规则的瓦斯和灰烬爆炸，据信这是由于浅层岩浆碎裂所致。然而，其触发机制仍存在争议。鉴于对火山源过程的了解对于未来喷发的风险评估至关重要，因此本研究旨在阐明这些过程。我们使用来自于2018年在危地马拉的桑蒂亚圭托火山建立的永久地震和次声网络的数据以及其他临时站点，包括在2019年1月进行的为期13天的野外调查期间部署的地震阵列，来分析和解决导致破裂的碎片源特征。瓦斯和灰烬爆炸。地震数据的收集距离为4。离爆炸口5 km处，在爆炸前2-6 s内显示出微弱的地震信号和相关的主要地震信号。为了解析地震信号的源位置和起源，我们首先使用环境噪声分析来评估地下的地震速度，然后使用二维频谱元素建模（SPECFEM2D）来模拟地震波形。分析的数据显示了阵列下面的两层结构，其中有一个浅的低速层（v_s = 650 m / s）在较深的高速岩石（v _s= 2,650 m / s）。使用这种速度结构，使用阵列和粒子运动分析来限制可能的震源机制和深度。模拟和观察到的地震数据的比较表明，前兆信号与RZ平面中的质点运动有关，指向顶峰下方约600 m处的张裂裂缝。相比之下，主信号伴随着垂直的单作用力，该作用力起源于约200 m的浅深度。这表明Santiaguito的火山爆炸是在自下而上的过程中进行的，在该过程中，深部会产生拉伸裂缝，并使气体快速上升，从而导致随后的爆炸。结果表明，Santiaguito的爆炸并非来自单个震源位置，而是来自可能与岩浆破裂有关的一系列过程，气体的窜流和聚集，以及破碎。我们的研究为在Santiaguito进行进一步调查提供了良好的基础，并显示了将地震观测值与针对复杂介质计算的合成数据进行比较的价值，以详细调查导致全球各地其他火山中发现的富含气体烟灰爆炸的过程。